West coast put in measures and shut down much earlier and quicker than out east and in general the population is far healthier, less obesity, less underlying issues. Washington had some of the first infections and has done a great job containing. My province here, BC, has pretty much nipped this in the bud too, with mostly voluntary measures.
As an aside, there has been some theorizing that the strain on the west coast came direct from China early on and is less virulent than the strain that passed through Europe on its way to New York and the eastern seaboard. It’s a possibility and would help explain the massive discrepancy in death toll (and death rate too)... but it also sounds awfully convenient for Chinese propaganda machine.