An optimist would say that's exposed so you can wipe it clean, a pessimist would say that's exposed so you can refine your profile to be better advertised to.
Ad networks (like me!) use demographic, psychographic, and behavioral data to target most display ad campaigns. I have run campaigns specifically sold as "market to Nigerian immigrants living in America" or "moms 25-35 interested in beauty products." And even when not specifically targeting those audiences, one can often find surprising performance pockets from these audience intersections- good for my performance and useful info to bubble back up to the advertiser.
And... guess who's the current biggest display ad platform?
Not everyone in the world can be assured their human rights and exposing personal information can lead to persecution. Therefore, there is a risk attributed to this data collection, at least for some. Not everyone is willing or able to take these risks.
While I can agree that this data may be useful for both customer and advertiser, its potential misuse should not be ignored. And when these networks deny the use of pseudonyms, they force their users to take (unnecessary) risks.
On the flip side, that's a confounding factor that makes it hard to compare Facebook to Google in terms of some type of battle for advertising dollars. For the time being they should both see revenue growth, irregardless of who does a better job.
Google understands that ignoring competitors , even niche ones , can be a long term risk. So they work on controlling all the advertising market. I think that's also the biggest reason behind Android: google makes very little money with it. But it's a great defensive strategy.