You have a point. The thing is, with gamblers they prefer to have another person playing in the same table. If the casino put an AI in there instead, it'll be like a noob playing chess on max difficulty - you'd feel very frustrated.
If it is known that an online casino used an AI, that could destroy the players' trust. How sure would they that not all "players" are AI and these are putting an act? After all, it's all virtual, you can't confirm who those are. It'll be like the Truman Show except with AIs.
I understand your point here. But it is never going to happen because this will cost a casino all its users. You just cannot win from AI if its on the other end of the table. Better go through the story of world champion Lee Sedol and vs. the AI robots AlphaGo and you will be surprised to know that the world champion could not win from the AL robot. So the casinos will not do that but can make use of AI in other different activities.
That's what I suggested they could attempt to do. Let's say there's only 1 human on a table, they can have the AIs on various difficulty levels that makes it not impossible for the human to win. Basically like playing Poker Superstars, it can still be an enjoyable game and the human might not notice.