Whether it's in the Terms of Conditions or not, general "no multiple accounts" rules punish players more often than anyone looking to abuse the actual site. Rather than target a symptom of a problem (i.e. multiple accounts from promotion abuse) they could just simply leave it at "don't use multiple accounts to abuse giveaways and promotions". The sweeping general term lets them do shit like this. What if a player, in one situation, comes back to the site after a year forgetting their previous account details? How about if they lose access to the password and email of an account? Any number of scenarios could be arbitrarily created, but that's not the real point: it's ToS like this, like the rollover requirements that some casinos use to "prevent money-laundering".

Masquerading as rules to prevent abuse against a minority of players, they in turn are used against every player.