I'm not sure why you were down voted to begin with, it's a valid question seeing how old many of GA engine designs are and how reliable modern internal combustion engines are. There's tons of advances in engine technology that isn't ported to GA aircraft for a lot of reasons, the biggest I would say is cost of FAA compliance and the insurance liability of failures. If your car engine fails on the highway you can still come to a safe stop. It's an extremely unlikely thing to happen on a modern car, but it's still possible (e.g. a cable is loose and disconnects the ECU). If your aircraft engine stops (which is also extremely unlikely, given the amount of routine maintenance it goes through to be considered airworthy) in the wrong phase of flight you're going to crash and possibly die.

Every plane you fly in commercially has at least 2 extremely reliable engines, and each one is certified to be able to handle flying the entire plane safely for an extended period of time to make it back to an airport in case of failure. The certification is called ETOPS [1], if a plane has 90 minute ETOPS certification it cannot fly more than a 90 minute flight from an airport. This appears to be a low-cost method of having a couple of minutes of safe controlled flight in case of a failure, that difference can make the difference between life and death for a GA plane.

This reddit thread has some good responses as to why Honda (who probably produces more engines in a month than Lycoming has in decades) doesn't make GA engines:

https://www.reddit.com/r/aviation/comments/1lxlco/why_doesnt...

[1] https://en.wikipedia.org/wiki/ETOPS