Having a Facebook account and verifying KYC on a platform isn't the same. Facebook doesn't verify your identity in the first place. Facebook won't know if you are using fake information to create an account. But, Once you create an account on a casino and you have to submit KYC. You cannot submit fake information to verify your account. On top of that, You cannot compare a facebook account with a KYC. Nobody on the internet knows if the account is real or not.
But almost everyone will input their real name and other information because they're still young and don't know about privacy matter, you can change your information but it doesn't make facebook wouldn't record all of your original information. You can't change all of your information too e.g. they will restrict you to change your username. In the last few years ago, there's a rumor where facebook sold their users' data or got hacked.