I get this. But as far as I remember I did only need a Facebook account but also my phone number. I don't think many people have more than one phone. And more importantly if you really want to you can set up multiple Facebook accounts just like with your email.
But I get its ment to bring value to your account.
The thing with email is that it's very easy to create instantly thousands of new accounts. Fake FB accounts are much harder to make, although still possible.
By the way, it's also possible to buy a new account with BTC or LTC: https://steemit.com/steemit/@anonsteem/bypass-steemit-email-phone-verification-with-anonsteem-over-200-users
I've recommended AnonSteem for potential users who can't or don't want to use phone for making a new account.
Very good to know. I will bookmark it. Thank you very much.