This how almost all HS swimming works. HSs don't have pools and the season is short-ish. Why would a HS rent a pool for 2-3 months to train a bunch of kids that already have a coach and a pool? Actually, I've seen what happens, you get a lot of kids literally new to swimming trying to be on a swim team. Its not pretty. That's why its not the norm.
As for football, they don't *play* all year but too many coaches now discourage or prevent those kids from participating in T&F by having so many offseason activities.
I agree about the coaching salary and such. Football is not going club.
The weird one for me is girls softball. That has tilted to club (at least here) and it makes no sense. There is no future or careers or money in softball (right?). What is the attraction of ditching your school team to play games hours away every week in front of no people for a result that nobody will know or care about? And the coaches spending years with these gals teaching them skills that have no real world applicability and which won't be used beyond HS or maybe college for some?
My guess is a factor is cliquishness where girls want to play with girls they always played with even if they attend different schools.
You can make arguments for sports being club based (some even good) but winning a league or county or state title has to be more meaningful than beating the Ogdenville Maulers after an 8 hr drive.