Every now and then there are some people who try to innovate in this space. Example: The guys from corsairpower (https://corsairpower.com/) who put a marine engine in a Cessna 172. However, it seems like they get stuck because of small market size, regulations and incumbents who don't want the status quo to change.

Don't forget that the incumbents will fight to keep regulatory barriers high.

I'd read this blog post.