A big factor is that battery storage wasn't there technologically until recently. You could cover Arizona in solar, but that just pushes the price of power down during daytime hours to $0. It doesn't help during the pinch times of late afternoon through sundown, when everything is still really hot, but solar produces significantly less. We need tons of batteries to store the excess solar from mid-day until the evening. Those batteries are being built very fast, but at the scale we need them, it will still take years.

This story is also a good illustration of why local government matters. National races get most of the media attention, but your personal day-to-day is more affected by your local government.