New York and Pennsylvania are two states with the most drive-in theaters in the country, so it's no surprise that there are so many drive-ins to choose from on the East Coast, many continually operating since the 1950s.
The South is prime Car Country, so it's no surprise that the drive-in theater format is still (somehow) alive down South.
I love that the Midwest still has so many drive-in theaters, because they all seem to sell the best midwestern grub at the concession stand, like cheese curds, bratwursts, and polish sausage (!)
The temperate climate out west makes it ideal for outdoor movie theaters, with several drive-ins managing to operate year-round.