Not questionable at all- it's a gold mine for knowledge of value to advertisers. Every post, like, etc. on Facebook is spontaneously coming from a user. You don't have to infer what people love or hate based on browser and search history, you just let them tell you (and all their friends) what they love or hate. They're literally telling you what you should advertise to them, it doesn't get better than that for businesses driven by ad revenue (not a negative judgement, just an observation). Of course Google would want that data, and of course Facebook would want to prevent them from getting it.

All of my local recommendations (handyman, local photographer, where to buy tomatoes) have now shifted to facebook groups. I no longer google handyman in blah, xyz. instead I go through my saved posts in FB.

This is along with local city news and news from friends and family that is all on facebook. e.g. One of my colleague's (and friend) kid was in ER last weekend so on Monday during standup I was able to tell the rest of the folks that he was out due to family emergency without getting an email from him...