Speaking as a parent of a daughter who is now in high school, in the California public school system, I have to ask:
Where would you get the money? The reality right now is that in every school district in California, and most of the districts in the USA, schools are hurting-- BADLY-- for funding, to the point where teachers are being laid off, class sizes are being increased, some classes on both the college prep end on the vocational end of the spectrum are being cut, and things like field trips are being cut.
Swimming pools are horrendously expensive compared to other kinds of athletic equipment. Their maintenance is very high, and the liability insurance for swimming pools is astronomical. The benefit of having a pool is not commensurate with the cost of having one. Swimming pools? Sure, they'd be nice. And that's exactly the point: a pool is a "nice to have" item, not a "need to have" item. You don't go out and buy "nice to haves" when you're having to cut your "need to haves" to the bone.