Since casinos are not giving any kind of free money and they have a house edge that guarantee the win for them in a long run no matter where do you bet or from which account, i.e. They aren’t either losers or winners. It’s usually used to prevent spamming by bots. The idea is that why would a bot use dual account while they can change seeds and do everything from one account?!
If you are an operator of an investment kind of project like gambling casinos or exchange you don't want your users to have multiple accounts in case there is a giveaway, bonus, or free perks it will be a source of abuse you want to implement fairness on your site and it will not happen if your users have multiple accounts that are all that I can't think, gambling operators should manage their project with fairness and equality.