I'm surprised people came up with this.

It's also surprising how big flaw was left in the referral system.

I imagined people would instead start creating Steem accounts, upvoting them a bit so they reach rep 30 (or more) and then just refer to themselves.

It wouldn't be a big thing to create a system which creates a lot of accounts, posts random shit with them, upvotes them till rep 30 and then just get the referral bonuses from yourself.