Back when I was growing up, schools didn't close unless the roads were physically impassible when the superintendent got up that morning.
I imagine that the reason why most pools close/reduce hours at this time of year is because recreational swimming is widely considered a children's activity. For adults, it's generally an exercise/competitive activity for some reason.
Owning a pool, they are a pain to keep up after Labor Day. Leaves are falling off trees, air temp is getting cooler, and thus water temp gets cooler. Chemicals in a large pool are pricey when no one is using it. I'm closing mine in less than 2 weeks, and I bet after today or tomorrow I won't be in it again, but will still have to test the water and maintain the chemicals, run the filter, etc.
For kids, they are also getting into fall activities & sports, and have less time devoted to pool activities. Plus, they're probably tired of it. I can hear it in my own neighborhood: Around Memorial Day, you can hear kids at other houses having a blast, jumping and splashing. By late August, even though it's still 90 degrees, there isn't a peep coming from those other houses, except for outdoor radios.
While they're nice, pools are a pain. Basically it's covered 8 months out of the year, and I have to tend to it multiple times a week, if not every day, when it is open. Too much rain? Gotta pump it out. Too little rain? Gotta add water. This year it actually wasn't too bad - only once did I have to pump some water out from too much rain early in the summer, and I was able to get all the way until late-August before I had to add water again, even though it's been fairly dry in July & August.
I never go to either one. You know that sign, "Welcome to our OOL! Notice there is no 'P' in it!"? Well, due to little kids whose parents don't teach/supervise them properly, our neighborhood definitely has a POOL, not an OOL.
Something you notice in Vegas: There's a lot of 20 & 30-something year olds in the pools. They are in there all day, drinking their beers and margaritas. Yet, no one ever exits the pool, all day long. They might as well call them
All I can say is...don't drink the water!