Smoke is a big reason
I like that Disney caters to families, the whole premise from Walt is a place the family can be together. Yes, there are some adult only venues, and some kids only venues, but casinos offer a whole different level to the adult-only emphasis.
Drinking is also emphasized for obvious reasons. I am worried there would be a lot more drunk passengers on the ship.
I worry that if it is done on the Adventure, it will be replicated elsewhere throughout the fleet. That means casinos will likely come at the expense of other venues that I do, or my children would, frequent. (I don't imagine them removing cabins to create the casinos).
Now to be fair, the Adventure is a much larger ship, and can absorb the space hit better than say the Magic, but I just hope Disney holds to the hard and fast rule of no casinos.
Disney has stayed away from some of the slimier cruise ship elements like casinos, and no longer does art "auctions" at sea which are notoriously deceptive. I think that focus on family entertainment has done them well, and they'd be wise to continue it...