As a generational expert with over 25 years in the field, Alexis Abramson has heard about all there is to hear from brands trying to appeal to various age groups. From baby boomers to Generations X, Y and Z—pick your group, and she’s researched them, written about them and (probably) lectured brands on how to attract them, too. In recent years, a good many of those brands have had their sights set on the generation born between 1981 and 1996: millennials, aged 23-38 today. That’s because at 83.1 million, a full quarter of the U.S. population, millennials are now the largest single consumer group out there. Simply put, few companies can afford not to court them.

But ask Abramson how brands feel about millennial consumers these days, and the answer might surprise you.

“There was a great deal of interest [in millennials],” she said, “but there wasn’t as much due diligence around that group. We’ve generalized them as a certain type of person, [but] the reality is the rubber is meeting the road. Companies are starting to understand, ‘Wow, we’re not getting the ROI we thought we might.’”

Abramson isn’t a voice in the wilderness. Her analysis joins a growing body of evidence that suggests that millennial consumers, for all their size and savvy, haven’t exactly been the boon that many brands expected them to be. That’s not to say that millennials aren’t all those compelling things that innumerable articles and reports have brimmed about: digitally native, mobile oriented, media savvy, politically progressive, ethnically diverse, well-educated and culturally savvy. Millennials are, indeed, all of these things.

Source: Deloitte

But a troublesome detail has been persistently overlooked over the last decade of wooing this crowd: Millennials—many of them, anyway—are strapped for cash.

That’s one of the takeaways of a brand new study from Deloitte’s Center for Consumer Insight, which surveyed over 4,000 American consumers to determine their current consuming habits. And when it came to millennials, one statistic stuck out: Since 1996, the average net worth of consumers under 35 has dropped by 35%.

Surprised? So was Kasey Lobaugh, Deloitte’s chief innovation officer for retail and distribution. He highlighted that while companies have been busy focusing on millennial spending habits as they relate to personal identity or cultural factors, what they really need to pay attention to is the millennial wallet.

“[If] you think about the narrative in the marketplace around the changing consumer and the millennial, there’s very little focus on the behaviors that are driven by economics,” he said. “There’s a narrative driven by some kind of cultural change. One of the things that really shocked me is that the economics of the consumer are really the most singular driver of behavior.”

In other words, he said, “people behave more like their income than their age.”

Was marketers’ faith in millennials misplaced?

In the years since brands began buzzing about millennials in the early 2000s, a number of rosy generalizations about them have taken root. Take this appraisal from the Obama White House published in 2014: “Millennials are a technologically connected, diverse and tolerant generation. The priority that millennials place on creativity and innovation augurs well for future economic growth, while their unprecedented enthusiasm for technology has the potential to bring change to traditional economic institutions as well as the labor market.”

But now that millennials are in that labor market as fully vested consumers, a slightly soberer picture is emerging about their buying power. The problem is not their size, as millennials represent a larger consumer group than the baby boomers. And it’s not the block of money they control, as millennials spend about $600 billion a year and are on track to spend $1.4 trillion by 2020, according to Accenture data.

But a troublesome detail has been persistently overlooked over the last decade of wooing this crowd: Millennials—many of them, anyway—are strapped for cash.