multi accounts not only in casinos but even on all other sites that provide benefits such as referral programs, usually there are always greedy people who commit fraud by using the referral program, but usually not many get away and they are always caught committing fraud. usually the casino will immediately ban their account and their money is also frozen.
multiple accounts on gambling sites have existed for a long time and they are just irresponsible people who want profits by taking advantage of bonus programs and referral bonuses, that is one of the actions that is detrimental to casino sites.
but fortunately nowadays many casinos have a team or system to detect such a cheating system.
so any multi account cheating will be immediately caught by the review team and ban the account immediately.
Unfortunately that won't end anytime soon neither. Because there are bonuses and rewards and so forth, they will keep on trying to abuse it, casinos are one of the most abused websites in the world because they are not as protected as other websites, if a user abuses your system or even hacks into it and steals all the money, governments and justice departments won't be rushing in to help.
If you have a lot of money then you can hire the best lawyers, but in most cases it won2t work. This is why casinos take their own defensive actions and these are just some of it, try to ban multiple accounts whenever they face with one and have to stop them.