It's all about state legislatures supporting or fighting the industry. If you have a government that puts artificial barriers in place that devalue investments by homeowners or commercial farms, you're not going to get much installed capacity.
Oil itself doesn't really compete with solar. Solar is used for the electric grid and oil is almost never used for the electric grid save a few outliers (Hawaii used to be one of those outliers, not sure about now). Natural gas, admittedly the same industry as oil, does compete with solar.
So I agree with the others that say this is state politics. Texas should have far more dual use land with its wind farms and solar capability considering much of the land can't even be properly used for farming or ranching.
My area is full of solar farms. I pass three of them (and a wind farm!) on my drive to work. From what I understand there were great leaps in renewable energy here a few years ago thanks to proper legislation and subsidizing farmers who put land towards it. There's been some pushback recently, mostly from the top because it supposedly "interferes with local military programs" and from the bottom because we don't see any of the energy produced being used locally. But they're still here.
Though size, population and geography obviously plays a part, this seems to have a lot more to do with politics than the amount of sunshine. I'm most surprised that New Mexico didn't make it.
One of the problems is that most individuals and businesses don't go 100% solar, and somebody still has to pay for the overhead and maintenance on the existing grid. Some states allow electric companies to add a surcharge to any customers who supplement with solar power, claiming that without the charge their other customers will have to make up the difference. They say that puts their non-solar customers in the position of subsidizing those who use solar power. The power companies worry that if enough people go solar, they won't be able to maintain their systems for those who cannot or choose not to do so. The solar industry is still young enough that those issues haven't yet been worked out in many states.
So I agree with the others that say this is state politics. Texas should have far more dual use land with its wind farms and solar capability considering much of the land can't even be properly used for farming or ranching.