It also is really hard to profit from ONLY meaningful data thus the death of things like RSS feeds. Can't shovel advertisements, trackers, and spyware down someone's throat just sending a nicely formatted HTML table that the client decides how to display and use.
Truly, good, semantically meaningful and correct HTML tags used without tons of obfuscating markup to appease some maniac's absurd sense of aesthetic (my own included) would be a pretty sweet API to consume. There's also the subtle reality that nearly every single worth a shit UI designer app, is under the hood, using XML-esque format to describe what you've done... which is mostly akin to "put a table here, with a given convoluted datasource."
Things like yahoo pipes come to mind as something that was frankly awesome, and totally failed to find a viable market. Likely because you can't shovel ads down someone's throat and forcefully track their every move sending them only things they want to consume.
The continued gating of data is only going to exacerbate the problem; I fear that companies like Facebook (though it's far from the only guilty party) advocate for privacy solely to protect their data monopolies. It will soon become impossible for other players to enter the market because it'll be rightfully illegal to collect or mine that data. Yet, companies like Facebook will still have access to it. I have zero reason to believe their intelligence systems are going to "unlearn" from illegally sourced data or that they can even meaningfully remove it (you really gonna go remove data from those tape backups?).
I was reading the other day about folks who want to do link previews but its essentially impossible if you're not facebook because your bot is instantly blocked. So while organizations like Facebook and Google are allowed to freely pilfer the internet of resources for their own bottom lines... and applauded for it. Anyone else is looked at like scammers and frauds. But.. I'm starting to digress and ramble; so, I'll end it here :)
Edit: Slight updates for grammar/readability.