Why would this forum want to tie accounts to social media? Very few people would use their own personal accounts and just create new ones so it's pointless. All you do is punish regular users and trouble makers will just do everything they can to bypass them.
How is it punishment?
Edit: To answer your first question, the admins always claim the difficulty in enforcement is why they allow alts. By tying account to a social media account, you are increasing the barrier to registration.
Can people go around it? Yes. But it is harder.
If you use a public proxy within the same IP range to create social media accounts, it will be flagged. Additional verification is required.
If you create more than x number of social media accounts from the same IP range, it will be flagged.
If you login to more than x number of social media accounts from the same IP range, it will be flagged.
Logging off accounts will leave cookies in place as well, and people will always get their social media + account combinations mixed up - which gives admins more information to ban alts.