Tribal-operated casinos have realized that that's a very good way to bring in traffic to their casinos. They're looking for people to come in and spend money on gambling, not just go to a concert.
The stigma of playing in casinos is long gone. They've improved over the years.
You're benefiting from the explosion of the casinos. They give artists chances to be seen in new markets, and the casinos can pay a good amount of money to bring in these acts.