That's just because the way to complain is built-in. Google can do whatever stupid thing they want to Gmail's UX with way less complaints - because what will yo

That's just because the way to complain is built-in. Google can do whatever stupid thing they want to Gmail's UX with way less complaints - because what will you do, write an e-mail about it? :) Also because the average Facebook user is not really computer literate, and such an user develops UI eidetic memory rather than functionality thinking - so moving a button leaves them clueless.