Consider this:
What other modern engines use magnetos instead of electronic ignition?
What other modern engines run on leaded fuel?
What other modern engines use carburetors instead of fuel injection?
What other modern engines use manual mixture control instead of closed-loop automated control?
What other modern engines must run at air densities from below MSL to 25,000+?
What other modern engines are air/oil cooled instead of water-cooled?
The list goes on and on. GA has boxed itself into a corner with our application requirements. As a result, we're on a technological island all by ourselves, with no other industry helping to share our development and tooling costs.
As a point of comparison, Jasper is a company that rebuilds automotive and marine engines, differentials, and transmissions. Every year, they rebuild 65,000 engines and 75,000 transmissions. Compare this to the GA market as a whole; there are only ~ 200,000 total GA aircraft, so if each one gets a rebuild every ten years (unlikely), it would still be less than 1/3 of one automotive rebuild company's volume.
https://www.jasperengines.com/about/about-remanufactured-engines/ [
Full disclosure - I got a rebuilt V-10 from Jasper about15 years ago. It ran flawlessly for more than 100,000 miles until I sold the SUV it was in - longer than the OE engine had survived.]