Small GA airports out in the middle of nowhere can come into being, but it's rare, and the whole GA field is aging out and disappearing (both the pilots, planes, and people).
A big part of that is the regulatory environment. For example - I have the interest and means to get my PPL. I'd love to do so, but the FAA considers ADHD to be a disqualifying medical condition.
Yeah, that's the problem: once they close down and the land gets sold, it will typically get developed and once that happens the land isn't coming back unless you have a Detroit situation. It's not like suburbs have lots of empty space for an approach and a strip. Even if there were, NIMBYs would prevent one from happening.