If the casino site has something like this mentioned in its ToS, then of course they will not allow it. All casino sites have almost the same ToS with only a few changes. And those changes may be due to the rules and legal processes of a country and some personal decisions of that casino site.
Legit companies must write their own ToS, and if they do like you said, it is like plagiarism, that can be used as one of evidence against them. If a company has a plagiarized ToS, it can be very harmful for their reputation if it is detected anytime by community.
You perhaps implied that there are similar terms in ToS while there are not many different terms, but surely ToS must be written authentically by a company team, not copy and plagiarize.
If multiple accounts are prohibited then if someone is using multiple accounts and their security system can track it then they can ban that user or demand kyc at any time because they have clearly written it in their ToS. So first of all read the ToS then start gambling on a few sites if you are a conscious gambler
I'm doubtful that any casino allows multiple accounts on their site as this action is very dangerous for their business. It can lead to many types of exploitation and abuse like bonus in deposit bonus program, contests and other cheating activities. It's reasonable why all casinos are against multiaccounting on their platforms and this actitivity is universally not tolerated by companies in online gambling industry.