I would say though it's kinda hypocritical that casinos enforce this rule sometimes to withhold big wins. At least they should close the account and teach a settlement with the punter to find an acceptable solution for both parties.
That's my problem with the casinos too as they mostly enforce this rules when someone has won a big sum from the casino. There are many other multi accounts but they aren't doing anything about them until they have a reason to denied a player of his win. They're being greedy because some gamblers won't know they have multi account because they have forgetting about them for many reasons. I have opened an account with a casino because of a giveaway I won and need my username to claim my price, after many years the casino became popular I wanted to gamble on their casino and can't remember my email or password hence I needed to create a new account with them. If I was to be lucky and win a large sum, they'll then use this rule of not having multi accounts to denied me of my money when I didn't do it Internationally but my side of the story won't be held then I lose.