I first met Drew Houston four years ago, when Dropbox, the file storage and synchronization company he founded in 2007, reached 25 million users. Dropbox was in the midst of a growth spurt that has carried it to more than 400 million users, and a valuation of $10 billion in private markets. Its trademark, then as now, was its fast, simple syncing of files between computers and mobile devices. It looked like an incredible business in 2011. It looks much less so now.

At TechCrunch Disrupt in San Francisco on Monday, Houston appeared on stage to discuss the state of the business. Much has happened since Dropbox became one of the most highly valued companies of its generation. The cost of file storage, which Dropbox makes most of its money by charging for, has plummeted. Tech giants like Apple and Google, which once ignored file storage, built good-enough syncing options and began giving them away for cheap. Mobile operating systems evolved to hide the file system, making Dropbox look less like a command hub for your digital life and more like an arcane plumbing system. And new ways of working centered on messaging rather than file folders, led by fast-growing Slack, have raised new doubts about Dropbox’s importance to the future of work.

The most fragile of the private companies

It’s a set of circumstances that have led some to speculate that Dropbox will become "the first dead decacorn," as startup founder Alex Danco wrote last month in a widely read piece. ("Decacorn" is Silicon Valley-speak for a company valued at $10 billion or more, a play on the use of "unicorn" to refer to billion-dollar startups.) This month CB Insights, estimating that the company’s valuation is at least 25 times its 2014 revenues, called investors’ enthusiasm for Dropbox "irrational." Ben Thompson, the analyst and author of the Stratechery blog, calls Dropbox "probably the most fragile" of the 10 most highly valued private companies.

All of this goes well beyond the usual criticisms lobbed at fast-growing startups: that they can’t keep up their pace of growth indefinitely, say, or that their business model will hit roadblocks as they attempt to begin profiting from their users. Rather, it’s that the fundamental assumptions around Dropbox’s business have shifted, at the same time that the behavior of office workers is changing to make the product less relevant. It’s a criticism that could use a thoughtful answer — but at Disrupt, Houston was unwilling or simply unable to give one.

"The world's largest platform for collaboration."

Instead, he repeated his stock answer about competitors — "we’re not focused on that" — while sketching a vision of Dropbox that, while grand, was notably short on detail. "What we’re really building is the world’s largest platform for collaboration," he said. "We want to get to a place where it’s like any group of people in the world, any country, any company, using whatever technology they want, can work together without problems." Criticism of the company, he said, was simply a result of "confusion."

And sure, it’s early days, although Dropbox first launched an offering for teams in 2011. But have you ever attempted to collaborate on Dropbox? Its feature set is tiny: You can add a comment to a file, or share it, or move it. You can call up previous versions of a file. And four years after launch, that’s … about it? Compared to a communication-focused service like Slack or video chat, it’s barely a step removed from printing the paper out and asking a colleague to make notes in the margins. Sure, the ability to sync that file across your devices and share it with colleagues is enormously useful — but that’s an increasingly cheap commodity. (Compare it to Box, which has added project management, workflow automation, and other unsexy-but-valuable extensions to its core syncing service.) Or to Google Docs, which solve a wide range of collaboration needs for free.

At this point, Dropbox would point out that 130,000 businesses already pay for the professional version. And with hundreds of millions of people using Dropbox, the company will surely find its way into many more. But if their needs go much beyond basic file swapping, they’re likely to find themselves disappointed. And given the broad consensus that the real money is in businesses like theirs, they’ll likely wonder why Dropbox isn’t moving faster to meet them.

Dropbox will likely disappoint big businesses

Looking at Dropbox’s history, it’s fair to wonder whether the product team’s heart is even in enterprise software. The company was founded on solving an individual person’s needs — as a graduate student, Houston tired of having to transport his files on a thumb drive. As Dropbox grew, it acquired a slew of startups dedicated to personal media storage and productivity: Audiogalaxy for music; Loom for photos; Readmill for ebooks; and Mailbox for email.

To date, nothing has emerged from the Audiogalaxy or Readmill acquisitions. Mailbox is among the best email apps ever released, but it has barely cracked the top 1,500 iOS apps this year, according to analytics service App Annie. Mailbox hasn’t released a new feature since January; its blog was last updated in April; and its founder, Gentry Underwood, stepped down from his role as Dropbox’s head of design. (He remains at the company "in an unspecified capacity," Bloomberg reported in June.)

The result of the photo app acquisitions was Carousel, an app for archiving and sharing old pictures that the company launched with some fanfare in April 2014. At the time, it looked like a moderately more polished version of the iPhone’s Camera Roll, with better cloud storage. But since then, Apple has rolled out a new Photos app with much cheaper storage, and Google and Flickr have jumped in with more generous and full-featured photo services of their own. Carousel fell out of the top 1,500 most-downloaded iOS apps earlier this year, and its blog, once updated regularly with photo tips and tricks, has been all but abandoned.

What problem is Carousel even trying to solve?

Asked at Disrupt about Carousel’s lack of traction, Houston was characteristically dismissive. "People love using Carousel," he said. "Obviously, we’d like it to have a billion users. It still has a way to go, but it’s early. All these problems are big problems — we go after them because they’re hard and they’re important. If these things were easy and fast to solve, someone would have done them already." But what problem is Carousel even trying to solve, other than the persistent problem of Dropbox users who haven’t chewed through all of their free storage yet? What can Dropbox uniquely do with photos that its competitors can’t? Particularly when competitors are giving better versions of it away for free?

But to expect a grand vision from Dropbox is to ignore history. The company succeeded initially not because of a unique insight into productivity but because it wrote better software than its peers. Lots of apps let you store and synchronize your files; Dropbox was simply superior. I don’t minimize Dropbox’s achievement there — it benefited from tremendously clever software engineering and product design. That bought the company years to explore new products and businesses. And ignoring competitors was a strategy that served Houston well — most of them simply weren’t very good, and Dropbox’s laser focus on perfect syncing allowed it to vault far ahead of them.

But after years of investment and exploration, syncing files is still the only thing Dropbox does well. Steve Jobs knew this: he famously told Houston (while trying to acquire it) that his company was "a feature and not a product." As Dropbox rocketed to 400 million users, Jobs’ viewpoint was easy to dismiss. But as its rivals caught up, and Dropbox began casting about for its next act, Jobs has come to look more prescient. Dropbox’s consumer products are losing their luster, and their business products lag well behind their competitors.

There’s real value — billions in value, even! — in what Dropbox does, and it continues to employ some of the best engineers and product designers in Silicon Valley. But most companies never manage to do more than one thing well, which is why it’s important for them to focus on a problem people will pay lots of money to solve. No one syncs a file better than Dropbox — it was true four years ago, and it’s still true today. But as a "platform for collaboration," it’s woefully underdeveloped — and well on its way to proving Jobs right.

Correction: An earlier version of this article incorrectly reported that Dropbox had acquired PicJoy.

Small Empires: DAQRI wants to change how we work