Another issue with high school football is specialization. My youngest is a freshman. Of what I would consider 28 potential football players in his class, only 18 are playing freshman ball. In looking at the kids that are not there, 4-6 are in other sports (basketball and hockey) as their main sport. So they don't want to play football and risk injury.
20 years ago they would have played football to stay in shape and compete. So year round training has led to specialization causing many to drop.
Of the other 4-5 kids that aren't playing. 2/3 parents don't want their kids playing football. Concussions primarily.
Lastly, kids don't want to put in the effort. 2 weeks of 4-5 hour practices when it was in the 90's( I was surprised, we did not shut down any practices due to hear), versus being able to play video games or wakeboard losses a fair number.