As a politician, it is not desirable to be connected to the Mormon church (they want to put their finger on the scales, you have to tithe a lot, etc).

You want the credentials but not the cost, or you end up in a very hard balancing act with a lot of internal politics.

There are Mormon politicians in Utah - but not as many as you would think. It looks like currently three Utah districts have Mormon reps.

Locally you may see a lot more Mormons as the political balancing act is overall easier.