As far as I understand, the bigger casino is a FIAT one, which would make scamming more difficult since there are third parties (banks and payment processors) directly involved in the transactions. If something shady happens there is a chance to find mediation and get a refund. Or am I mistaken?
They also would need to keep some facade of legitimacy in order to use FIAT/ regular bank accounts.

It's not about FIAT or crypto since they are all operated by people at the end of the day. These corrupt people have powerful connections which help them get away again and again despite rising scam accusations.
True, scam casinos do not recognize Fiat or Crypto payments and 1xBit is a scam casino that has been operating for quite a while and until now no one has been able to shut it down and help solve all the fraud problems that have occurred.
Various attempts have been made to suppress the circulation of this casino scam, but the results are still the same, they even have a fairly large and active marketing community on several social media.
While up to 1xBit also accepts meaningful fiat payments outside of cryptocurrency bases, 1xBit is really spreading its wings to be able to fool more gamblers.