California was hit early but acted very quickly and effectively. They're also pretty wealthy so they could get equipment and supplies before there was really a rush.
Texas and Virginia had the benefit of getting hit when most people were taking this seriously (i.e. they didn't want to become NYC). You also have to consider public transportation use which is way higher in places like Seattle and Chicago than it is in Dallas, Houston, etc.
So again it's mostly about exposure: density, travelers, being in contact with travelers, being in contact with people who've been in contact with travelers, etc. How quickly shelter in place was ordered (getting a testing system set up would also have worked but you have to act even faster and spend upfront money, which of course we were never going to do) has a direct effect in exposure. And then it's all about how well you get supplies to treat the infected.
What makes Washington, Illinois, and Michigan so bad compared to Texas, Virginia or California?