Right, but that's the problem: with no market, things can't get cheaper because there's no capital to innovate with. That's why General Aviation is in a death spiral (ironically, since "death spiral" is a GA term): fewer people buying planes, companies exit the market and remaining companies have to charge more per-plane to cover fixed costs, GA becomes more expensive, fewer people buy planes, etc.

Why is nobody willing to take a risk to revive this market? If the only thing preventing a revival is cheap planes, couldn't someone get some investor to pay for all the certifications of their modern, fancy, efficient, cost effective plane, and then sell a million of them?

That is essentially how any new industry works. EV's were too bad/impractical/expensive until Tesla decided to take the risk and put down the capital to make them mainstream. Why can't/doesn't someone do the same for GA?

the FAA does not want to see it happen, and they have the power to drag their heels.

Yeah, I would totally get a PPL if it wasn't at minimum $15,000.