I do not disagree with vanesha that bonuses are not the only cause that people have numerous accounts. Some gamblers, even in the absence of such, believe a new account will start afresh their fortunes following a losing streak. It has more to do with psychology than with rewards. With that said, it is not easy to create multiple accounts within one site. Casinos trace wallets, bank information, IP, and even devices, thus having different bank accounts is not always sufficient. Majority of players seeking to have several accounts end up using alternative sites. Deleting bonuses would decrease the motivation to some extent, although it would not prevent players to use multiple accounts because the luck and state of mind are also significant in gambling behavior.
I have seen that situation with my friend as well. He played on slot sites for some time. What he found was that every new account would have a chance to get a big multiplier in the first few spins. So when he felt he wasn't getting a good multiplier, he would create a new account on the same site. I don't know if it's true, but he said that all new accounts were fine.
Bonuses aren't the only reason gamblers create many accounts. But there is a big opportunity when casinos offer welcome bonuses, which gamblers often take advantage of by creating multiple accounts.
