Tech investors took a shine to media companies in 2014, reversing their longstanding aversion to the news business.

Vox Media picked up $46.5 million in a round led by General Atlantic in November. Vice Media raised $250 million from Technology Crossover Ventures in September, following a $250 million investment from A&E Networks in August. BuzzFeed raised a $50 million round led by Andreessen Horowitz in August.

Even more eye-popping than the amounts raised are the valuations: Vox is reportedly worth $340 million, BuzzFeed $850 million, and Vice $2.5 billion.

(Disclosure: VentureBeat’s a media company too, and we raised $2.6 million earlier this year, but our valuation and business model are both pretty distant from these giants.)

Numbers like these got me wondering: What’s going on here? Traditionally, venture capitalists want little to do with advertising-supported media companies, which cost a lot of money to get off the ground, don’t have obvious exits, and tend to grow more slowly than your typical software or hardware company.

There’s no doubt that all three companies have shown tremendous growth when it comes to pageviews and unique visitors. But the end game is less clear.

BuzzFeed, for instance, reaches 150 million people a month and is “consistently profitable” with revenues in the triple-digit millions, according to investor Chris Dixon, general partner at Andreessen. Let’s say “consistently profitable” means “just barely profitable,” because if it was throwing off enough cash to be hugely profitable, it wouldn’t need investment. And let’s assume “triple-digit millions” means something over $100 million. The company employs more than 500 people, including 200 editorial staff and a tech team of 100, although reports I’ve heard put its head count at around 800. At that rate, it’s spending between $65 million and $100 million on personnel costs alone. Add in rent, server maintenance, payments to outside consultants, and more, and it’s hard to see how there’s much profit left in that $100 million in revenue.

[Update 4:25pm: I wrote the above paragraph based on publicly-available information, but a Buzzfeed spokesperson tells me the company actually employs a little more than 700 people, reaches more than 200 million uniques per month, and is delivering 750 million video views per month.]

So how does BuzzFeed grow? The same way any giant media company grows: by increasing pageviews and growing its audience. The problem with that approach is that to grow your audience, you need to hire more content people. With a few exceptions, there’s a fairly linear relationship between staff growth and traffic growth — so unless BuzzFeed has discovered some dark magic (and it may have), I don’t see the profit margins growing much even if the traffic — and the revenues — continue to grow.

That may be why BuzzFeed now operates a division called BuzzFeed Motion Pictures, with a 45,000 square foot film lot in Hollywood — even though founder Jonah Peretti said a year ago that “we will NOT launch a BuzzFeed TV show, radio station, cable network, or movie franchise — we’ll leave that to the legacy media and Hollywood studios.” He’s probably looking for fatter profit margins, and homegrown cat videos (or feature-length cat movies) are one way to get those.

You could do a similar analysis on the other big venture-backed media companies. For example, Vox chief executive Jim Bankoff said in November that the company is “closing in on profitability” and would be in the black in 2015. But then, he also predicted that Vox would be profitable in 2013, and he made the same prediction for 2014, too.

All of these businesses remind me a bit of the old adage about buying widgets for $1.05 and selling them for a dollar — “We’ll make it up on volume,” the naive entrepreneur says. So how are Vice, Vox, and BuzzFeed different?

For starters, they may have business models that go beyond advertising. With the value of online ads dropping — and half of online ads are not even seen by actual humans — any business, news or otherwise, that bases its revenue solely on ads is going to be a short-lived one. BuzzFeed, for instance, seems to have figured out how to make native advertising plus social media promotion work together very well, turning it into a savvy marketing partner for brands. Vox is building a network of sites, with (I think) the aim of becoming a smarter, more tech-savvy Conde Nast, selling ads at a high rate and leveraging similarities between sites to offer bundled deals. Vice — I have no idea. Maybe it’s on its way to becoming a cable network.

Another key may be that they’re large enough to make significant investments in technology. BuzzFeed’s 100 engineers, for instance, could potentially create new tech tools — or a platform — that could substantially change the news game.

Still, I don’t see how any of these companies can wind up accelerating their valuations much beyond the current level, at least not without pulling something totally unexpected out of their sleeves.

Marc Andreessen himself said earlier this year that he’s more bullish about the future of the news business than anyone he knows. And to be fair, all three giants publish some outstanding journalism among the crowd-pleasing posts that they are perhaps more known for.

I wish all of them well because, as a journalist, I want there to be many lucrative options for employing people like me. As a reader, I value the journalistic work they do. (The GIFs, less so.) But as a business writer, I’m not convinced I see venture-worthy returns in any of these companies.