Many gambling sites offer their users various bonuses at registration, so if one person creates several accounts at such a site, he abuses the advertising campaign carried out to attract new users. Obviously, this is a deception of a gambling site in order to increase the chances of winning without attracting new users. Therefore, I would advise against abusing promotions on gambling sites as there is a high probability of detecting abuse and banning your accounts.
I have never thought of this before until you posted about it now, all I was thinking before is that multiple gambling users accounts is to discourage money laundering but you are not wrong at all that many people will make use of welcome bonus opportunity to have more accounts so that they can have more means to earn the bonuses, humans are very greedy but I have never thought of this before to cheat, now I have only one account on each site when I know that is always included in their terms and conditions, even if not included, I still only got only one account which is more than enough for me.
Sometimes a casino is also partly to blame. Most often casino sites can detect multi-accounts and other violations. But the problem is that they don't flag it. They don't even warn the gambler that creating a second account is a violation of their terms and conditions.
Most casinos hide behind their Terms of Service. They know that players don't read them, but they really should. It's your responsibility to know what's written in the TOS, especially the parts about multi-accounting, VPN usage, restricted territories, and even the restrictions that certain game providers place for particular locations.
But majority of the casinos couldn't care less about these violations. They would only act on it when a jackpot or a big win happens. That's the time they would inform the player that he does not qualify for the prize because of the violations.
If you win, that's when they will do a proper security audit of your account. While you are depositing money and losing, very few casinos will have a problem with that.
I have four accounts in the first fiat based gambling site Ilthat I registered back in 2014, I later opened the fourth one which is my main account up till this day, I have no motive of money laundering or cheating bonuses, it is not what I have even done before while not really considering bonuses. I did not read the terms and conditions until like 2 years that I opened the account when I was not busy at all one day and having a boring time which makes it came to my mind to read, all other accounts are now in everlasting disuse whole only one main account I have now per each gambling site. Terms and conditions are too long for many people to read, but it is the most important thing for beginners to read for not to fall into centralized site traps.