Actually 2FA would be the easy fix.
2FA aligns with the first rule of account creation.
Legitimate account creation that is. Where a mobile number is linked.

After that the internal account creation can simply limit the amount of accounts linked to each mobile device. There is no legitimate reason why anyone needs to have so many accounts on the same platform.

That is however, a sensible and intelligent way of combating the issue.
Such sense does not exist here. If someone isn't making money it's not going to work or even get implemented!