Many people are complaining about the ancient technology, but newer ones offer very few advantages.
An piston GA airplane runs basically at two speeds: flat-out for take-off and cruise. For both the fuel/air mixture is easily optimized to optimal, and the slow engines reduce waste. Benefits from EFI are decent but below 10%. Supercharging helps a lot at higher altitudes, but most planes aren't pressurized or carry oxygen, so even that has limited benefit.
The main benefit of the current engines are robustness: I know people who have even flown without oil or with a blown valve. Many experimental builders combine mechanical magnetos with electronic ignitions, partly for fuel efficiency but mainly to lower idle speed on the runway when landing.
The real difficulty is not technology but service. There are very few engine rebuilders, and they are happy with the current limited supply of engines keeping prices up.
And unless you built your own experimental plane, or you get an experimental where the FAA permits owner inspections, the main cost of flying is service on the plane.
Aside 1: many engines have STC's to run car avgas. All require there to be NO ethanol for its impact on the fuel system. The studies I've seen of those engines report bottom rebuild times more like 800-1000 hours rather than 2,000 hours, and of course a higher incidence of valve-related problems.
Aside 2: experimental planes are not a subculture. They form the largest number of new planes. The $200K+ alternates only go to the wealthy. And after 50 years of competing companies, only one has been the overwhelming success, in both popularity and numbers: Van's aircraft. They use old-style, simple designs and construction, and (mostly) old-style engines, preferring the Rotax for their RV-12.