I'm sure there are a lot of online cryptocurrency casino out there which are reputable even though they did not introduced their company here. But it is also my preference to play on casinos which are widely known here in Bitcointalk.
I suppose that is the case, but am I willing to take that risk when so many good casinos are advertising here? Most certainly not as I simply do not have the need to take that risk, which help us understand why so many casinos eventually try to make their presence felt here on the forum, as forum members and those which read it can afford to not use those casinos, while casinos cannot really afford to not try to convince those very same users to try their casino, and finally they may take the decision to advertise here.
Since this is a forum created initially for Bitcoin and is now for all cryptocurrencies in general, almost all the cryptocurrency casinos or gambling platforms are available on the forum, and there are some which aren't available or introduced here, they probably are not that popular among the crypto gambling community.
I personally wouldn't mind playing at a casino that is old and has been serving the community for quite some time with no issues at all but only if they have a provably-fair system for me to verify the bets initially just to have peace of mind.