no idea if this is the reason but they are being pretty forward about banning malicious users (cheaters, creeps) and you can't do that effectively if you just ban the throwaway user.

Interesting. But don't you have to attach a credit card to buy and play the game? They can use that to identify repeat offenders and probably other things as well. Other platforms solved the issue without accessing my entire social graph.

Just make a separate/dummy Facebook account. That's what I use.