It has nothing to do with price. I don't check luggage on domestic flights because of the enormous time lag for the airport to give me back my luggage. (There's also "United Breaks Guitars", but that's an independent problem)

If I could walk from the plane to the luggage area and my luggage was already there 90% of the time, I probably would check more things.

However, the US airports simply don't employ enough people to move the luggage around fast enough.

The is 100% correctable by employing more people. But some CEO needs another yacht, so they don't. So, I simply don't check luggage.