GA engines use low compression ratios and high displacement to generate power at lower RPMs, reducing mechanical stress and heat buildup that would be catastrophic during sustained high-power operations like climb and cruise. The need for low propeller RPM means designs either go for a gearbox-driven high compression, low displacement approach like Rotax, or the low RPM, low compression, high displacement route like Lycoming—and given these constraints, the good old Lycoming design isn’t all that bad.

(Edited for completeness)