that is the reason why every gambler must read the T&C that apply to gambling platforms, even though I myself sometimes still forget not to read the T&C before starting to gamble in a casino that I didn't know about before.
I think I know the casino you mean.

I used to bet at a certain casino and I didn't read the T&C after that I got some wins and wanted to withdraw my funds but the casino refused. after that i tried to contact service support and they said i have to bet 5x of my deposit amount.
after that i got the hang of it and i made my bet in sports betting and made it to bet 5x of the deposit amount.

with this incident I don't think that the casino is unfair or a scam but I was careless not to read the T&C before placing a bet. after all, casinos have rules that must be obeyed, and if we are careless, we don't read these rules and get rejected, it's our fault.
so to be honest i completely understand the casino. because every casino has its own rules and we as gamblers must comply with these rules.

so for me the rule is natural not a problem and in fact the casino is still popular today.