I thought this too, but most of the kids seem to be playing basketball, which is a winter sport, or track. I don't think the football coaches mind if a kid misses for track practice, plus I don't think spring football interferes with state track meets.
One factor that I think is important is the size of high schools in states like Florida and Texas compared to Ohio. Ohio I believe has 1 high school (Mason) with 3000+ kids, and probably less than 10 with 2500 in the state. Compare that to Florida, Texas, Georgia, etc where you get suburban Houston, Dallas, Atlanta, Miami (where a lot of the recruiting is done) schools with whole districts consisting of schools with enrollments of 2500-4000.
Point being, a school in suburban Dallas or Atlanta with 3300 kids is not going to be hurt as much if a couple of potential baseball players play spring football, or a couple of track guys miss a track practice. With the specialization you see in baseball, and the weather in the south that makes it convenient to practice spring sports year round, some of those kids probably already quit football by 10th grade. It's different than Ohio, where even most suburban Cleveland, Columbus, and Cincy schools have less than 2000 kids. 2000 seems like the magic number to build another school in Central Ohio. In Texas, everything is bigger, they love 3500-4000 student schools, makes the sports teams more dominant.