Yes, it’s not just an East Coast thing. A pretty simple search will show you that the overwhelming majority of Jews in America are Ashkenazi today.
Another thing I’ve noticed is that Sphardim seem to prefer bigger shuls, therefore there doesn’t need to be as many. Ashkenazim split into a bunch of little stiebels/basement shuls so that even in a town with a 50/50 split of Ashkenazim and Sphardim, the number of Ashkenazi minyanim might be higher. I’m totally generalizing, but I think it’s a pretty uncontroversial observation.