Tax evasion through multiple accounts could be a reason. But most players who play on crypto casinos do so to avoid paying their taxes. They can claim one account as their own, and never mention the rest.
Common reason would be abusing giveaways, referral and other bonuses which is always be a violation of most gambling site terms and conditions and it is just right for those users to get banned or prohibited.
Those cheaters does really believe that they can really outsmart the house but in reality they are always one step ahead if you do plan something.
That's true, if you look at "Scam Accusations" section, people are opening multiple accounts as their referrals. If their affiliate account wins a big bet, they get a commission on their main account. Think about it, the affiliate account may win or lose the bet that doesn't matter but a guaranteed commission will go to the main account. Cheaters are using these opportunities badly and abuse the system. The main reason behind opening multiple accounts is to take advantage of referral commission and giveaway/ promo code.
gambling sites should definitely have the features to detect potential multi-accounting. because these people know how to work around about this. so casinos should really be more steps ahead of these abusers. and if they caught someone, they can present a solid proof to that owner. because without solid proof, these users will be loud about scamming, ect. ..so they can get their ill gotten funds. security is one of the most important features in gambling. without security, they can easily go bankrupt from abusers.