In the last decade, the West Coast (including Arizona) has been lucky if they got 2 regional sites. For the most part, they've got 1. 2 a few times and the odd 3. From the early 2000s until the very early 2010s, they were getting 4 sites consistently, and if they didn't, it was almost always 3. It was 3 of 4 in Arizona, Southern California, Northern California, and somewhere in Oregon. Often, all 4.
I'm no fan of the RPI (in fact, I think it is ludicrous) and bias may play too big a role in rankings but it isn't affecting hosting sites this year.