Why not ? Facebook has a large number of userbase and websites can use Facebook as a leverage to promote their sites.
I think the advertising on Facebook should be displayed to targeted audience because we won't want children to see ads related to gambling.
But other than that I think there shouldn't be a problem advertising gambling casino on Facebook.
I think many casino platforms are promoting with a targeted audience setting to bring in new users, besides the gambling community in the Facebook group is very large so we have to be actively involved to interact in active gambling groups, but the problem may not be crypto-based gamblers.