Part of the issue is that a lot of propellers in GA are, well, simple.
We do have better designs available, but very fast you end up with either very complex manufacture (and thus price) for special aeroelastic propeller, somewhat less expensive automatically adjustable props, better engines (hello recertification! the big cost killer and what made G100UL so important). I do not know if scimitar prop blades require adjustable mechanism, but wouldn't surprise me. And then there's how to fit scimitar blade on some airplanes.
So unfortunately non-trivial even when everyone involved is all for change, because change costs a lot.
We do have better designs available, but very fast you end up with either very complex manufacture (and thus price) for special aeroelastic propeller, somewhat less expensive automatically adjustable props, better engines (hello recertification! the big cost killer and what made G100UL so important). I do not know if scimitar prop blades require adjustable mechanism, but wouldn't surprise me. And then there's how to fit scimitar blade on some airplanes.
So unfortunately non-trivial even when everyone involved is all for change, because change costs a lot.