Since some bonuses cannot be applied to accounts that have been created already and in use, you most likely cannot get the bonuses on them and so I think it's a reason some gamblers would want a second account on the platform but then some casinos do not permit such and so they actually could try restricting or deleting their other account so they can actually get to start the new account and fund it so they can be able to enjoy such bonuses.
I'm not even sure if deleting an account is even possible in a casino; some can actually allow you to do that, while some can't, and even if you have a duplicate account, deleting the account is not the best option since you might abuse the bonus system. If you want to be fair, the best thing to do is to contact the casino and tell them about your duplicate account and give them the go-ahead to help you get rid of one, and that should be done when you have not abused any bonus system before.