It seems to me that in many countries there is a sufficient number of gambling games that are still not represented in casinos and especially such games are many among card games, because each individual nation plays its own card games of chance. And they are somewhat similar to others, but sometimes have important distinctive features. I will not name the games that are in my country and they are not available in the casinos, but I am 100% sure that in every country there are such games.
one thing i know is that casinos can not list all these mentioned games in there casinos because they may become irrelevant to people that do not know about it or I've not heard about them. If fee of those games become available on casinos, even those people that knows about it may not even bothered playing it not because they don't know it but because they seem not to be interested. For the fact that we know something do not mean that we can be interested about it. No casino want to spend a lot of money of acquiring a game for it casino and there is no gambler ready to bet on it.