Comment by mschuster91

The lack of modern small airplane designs, especially engines, is the extensive and thus expensive certification process. Most of what is a "new" airplane usually is derived from a very old, grandfathered design.

The only real innovation for small planes is in the electric flight area - when you gotta do a full certification anyway as you're piloting an entirely new drivetrain, you can financially afford to be much more innovative on other parts of the design.