I think another important part is that solar has low minimum useful quantities and customization. Lots of the problem with nuclear power is that you only need ~100 to power the US, and each one takes years to build, so getting scale is basically impossible. With a 50-100 year lifespan per plant, that means you only get to build 1-2 a year, and you can't learn much from the 5 you've most recently started since they're still under construction.