Many utility scale solar plants are indeed being built out in the desert. The Antelope Valley and along the 15 corridor in particular, as they have the power distribution lines already in place. However even along 80 you’ll see a few.

They tend to be where high voltage distribution lines leave high demand urban areas, and the land gets cheap enough.

A lot of other places just need some high tension power lines, and it will happen. Permitting for those is a nightmare.