Unlike the UK, legal gambling in the US is pretty limited. It's only allowed in eleven states, and even in most of them, it's pretty limited. It's also legal in most Indian reservations, but they're as out of the way as the states for most Americans.

In particular, Frist represents Tennessee, where gambling is illegal. Nor are there any Indian reservations in Tennessee that allow gambling. So that wouldn't seem to be his reasoning. Also, he's been noted as voting and acting in a religious-right manner.