The main difference for me is maybe that I don't want to use anything coming out of the Facebook corner of the planet and hence I have no beef with them. If a page insists in only allowing me in if I have a Facebook account, it's usually trivial for me to simply do without said page.
It's kinda different with Google. Google offers a fair lot of services, some of them even very useful. And them constantly trying to shove some useless services of theirs up my rear is kinda annoying when all I want to do is use one of their useful ones. Part of this is due to them buying up a few of the more useful and/or entertaining platforms of the internet.
Facebook only did that so far with a select few, and (since I don't use any of them anymore, I can't really vouch for that) as far as I know, they don't use them to shove "oh, and hey, here, use that $craptastic_other_garbage_of_ours or you can't use $what_you_actually_want_to_use anymore" in your face.