Facebook acquired Instagram for $1 billion in 2012, and in the seven years since, the photo sharing app has gone from just that — a place to share photos with friends — to an entire video, photo, and shopping ecosystem unto itself. That transition hasn’t been seamless.

Today, we learned a little more about why. Facebook CEO Mark Zuckerberg and Instagram co-founders Kevin Systrom and Mike Krieger didn’t agree on the app’s future, and that’s why the duo left the company last September, according to a Wired cover story about the past 15 months at Facebook.

It’s a great piece and mostly centers on Zuckerberg’s intense internal privacy concerns and attempts to preserve Facebook’s dominance. But in some ways, the most interesting parts are the new details about what happened between the Instagram co-founders and the Facebook CEO. Wired says Zuckerberg stopped encouraging Facebook app users to post on Instagram, and instead wanted to keep them contained in the main app. Nicholas Thompson and Fred Vogelstein write:

A few days later [Zuckerberg] asked his head of growth, Javier Olivan, to draw up a list of all the ways Facebook supported Insta­gram: running ads for it on the Blue App; including link-backs when someone posted a photo on Insta­gram and then cross-published it in Facebook News Feed; allowing Insta­gram to access a new user’s Facebook connections in order to recommend people to follow. Once he had the list, Zuckerberg conveyed to Insta­gram’s leaders that he was pulling away the supports. Facebook had given Insta­gram servers, health insurance, and the best engineers in the world. Now Insta­gram was just being asked to give a little back—and to help seal off the vents that were allowing people to leak away from the Blue App. Systrom soon posted a memo to his entire staff explaining Zuckerberg’s decision to turn off supports for traffic to Insta­gram. He disagreed with the move, but he was committed to the changes and was telling his staff that they had to go along. The memo “was like a flame going up inside the company,” a former senior manager says. The document also enraged Facebook, which was terrified it would leak. Systrom soon departed on paternity leave.

Once Systrom returned from paternity leave, he and Krieger decided to make it a permanent decision, and the pair left the company. The news leaked to The New York Times before Instagram’s communications team had any idea of the news, and although the pair were cordial in their following statements, a story emerged that they left because of design and functionality disagreements with Zuckerberg.

Wired specifically cites Systrom and Krieger’s aversion to hamburger menus, or icons that unfold to reveal a variety of options. The hamburgers have overtaken the app since the pair’s departure.

In just the last year, Instagram has changed and added significant functionality. Profiles have been redesigned to feature more ways to contact businesses, with up to six options displayed. In December, the company accidentally pushed new navigation live that would made the feed horizontal instead of vertical, which the company chalked up to a “bug,” but also could have suggested that the company is experimenting with new ways to get users to engage with the platform’s content. Instagram has also continued to push into longform content with IGTV, and recently started allowing users to publish their IGTV content on their feed, which drives up viewer count but also bogs the feed down with more content. On a smaller scale, the company added features like “close friends,” that lets users share their story content to a smaller group of curated people.

Although the new Wired details aren’t much to go off, they continue to add up to the bigger storyline that Zuckerberg wanted more control over Instagram, as well as the ability to turn the app into a closer sister to Facebook. You can also see that in his March announcement about moving away from a public News Feed and toward encrypted, private messaging, as well as the recent decision to make shopping on Instagram even more streamlined. (Instagram has told The Verge’s Why’d You Push That Button that it wants to build everyone their own “personalized mall.”)

More generally, Instagram seems to be going the way of Facebook. It wouldn’t be unsurprising to see Instagram launch event features, like its sister app, or even in-app games, which would be a nightmare. But again, if Facebook itself is falling out of popularity with users, there could be a world in which Zuckerberg somewhat abandons ship and pushes every Facebook feature onto Instagram to see what works.