Yes the forum can ban any fraudulent activities project that is a threat to the existence of the forum and that was why mixers were also banned and I believed 1xbit has not been banned because it is gamblers they scam and they have been enough and a lot of warning threads have been created to warn gamblers to stay clear that one too is good enough for people to leave the scammers' den of 1xbit. Every old member of the forum must be aware of the this scammers casino so there should no too much arguments on this matter.
Mixers were banned as there are a lot of mixers scammed and ran away and also a lot of scam happened and at the same time there was legal activity against mixers. But gambling has nothing like that and that is why forum is not taking any action against 1xbit though they are a proven scammer.