Though it’s not exactly an apples to apples comparison, it was inevitable that relative newcomer Snap Inc (NYSE:SNAP), the parent company of messaging app Snapchat, would be compared to old-guard social media giant Facebook Inc (NASDAQ:FB). Owners of FB and SNAP stock have been trained to grade their pick by stacking it up against the name that’s most akin, and like it or not, these two companies are jockeying for the same advertising business; Twitter Inc (NYSE:TWTR) has pretty much been left for dead at this point.

Calling a spade a spade, Facebook has won the war. Snapchat made for an interesting effort to keep Facebook honest, but the 40%+ pullback SNAP stock has suffered from its post-IPO peak of $24.40 in March speaks volumes about what the market thinks of the company’s first couple of quarterly reports.

Yet, Snapchat has won the battle on one front: teens. Teenagers would rather use Snapchat, if only to avoid their parents who are using Facebook. Unfortunately, this is not exactly a demographic worth winning.

Teens Are Anything But a Panacea for Snap Inc.

The data (an estimate actually, albeit a well-founded one) came from eMarketer, a source of news and research about online advertising trends. The pinnacle conclusion was that, for the first time ever, the number of Facebook users would decline 3.4% this year.

Those teens are instead choosing to use Snapchat or Instagram. Snapchat’s overall headcount is projected by eMarketer to swell 25.8% this year and not just with big-time help from 12 to 17 year-olds. The 18 to 24 years-old user base for Facebook is also expected to shrink, with the bulk of them migrating to Snapchat or Instagram as well.

It’s not the end of the world for Facebook. Facebook also owns Instagram, so it’s retaining some of that coveted crowd. It’s not keeping all of it though, and like Snap, it’s struggling to adequately monetize its teen users.

That can come as a bit of a surprise. After all, the teen crowd’s (and the U.S. teen crowd’s in particular) spending power has been well-touted. Estimates suggests that the United States’ teenagers (between the ages of 13 and 18) collectively represent $208.7 billion worth of annual spending power. That’s a slightly misleading metric though. Of that $208.7 billion though, only $91.1 billion of it is earned by the kids themselves. More than $100 billion of it is their parents’ money—parents who aren’t swayed by Snapchat’s and Instagram’s teen-targeted ads they never see.

And, as it turns out, while the average teenager earns something on the order of $3800 per year, they’re more likely to spend it on food and clothing than experiences and digital downloads. Physical goods are tough to sell online.

At the same time, while the country’s relatively flush 26.8 million teens earning an average of just a little less than $4000 per year makes for an interesting talking point, it’s a market that pales in comparison to the $32,000 in discretionary income the average 35 to 44 year-old enjoys every year. The typical 45 to 54 year-old, where Facebook is increasing market share, isn’t far behind with their $28,000 worth of annual discretionary income.

But there’s one overarching metric that should really gnaw at SNAP stock holders who were otherwise excited to learn about eMarketer’s assessment: The ads aimed at the 18 to 24 year-old generate the lowest revenue-per-click for any of its demographic groupings. Granted, those clicks also cost the least to induce, but this millennial crowd drives the lowest margins and the weakest ad profitability for any of its age-group segments.

In other words, of all the users to lose, the 13 to 24 year-old sliver of the consumer market is the one Facebook doesn’t mind losing.

Looking Ahead for SNAP Stock

Sure, there’s an argument to be made that today’s teens will be tomorrow’s (proverbially) high-earning 30- and 40-somethings. Get them plugged into the Snapchat ecosystem now, and they’ll stick with it then.

That’s an assumption that more than stretches hope though. They might keep Snapchat as the social-media centerpiece of their lives. Or, they might outgrow it. They also might migrate to Instagram, which again, is owned by Facebook.

There’s also the not-so-small reality that Snap continues to lose money hand over fist, and is expected to do so for the foreseeable future. It may not have ten to twenty years for its teens to become high-earnings middle-aged adults.

Point being, if you own SNAP stock primarily because it’s doing well with teenagers, that’s just not a good enough reason.

As of this writing, James Brumley did not hold a position in any of the aforementioned securities. You can follow him on Twitter.