Pilots are free to offer commercial services; they merely have to obey a much stiffer set of regulations.

Flying privately is legitimately dangerous, whereas commercial aviation in the united states is very safe. Customers are in no position to evaluate the pilot or plane. Most accidents are due to pilot fault, often because of bad weather; offering commercial services that come with expectations of getting places increases pressure to fly in weather or circumstances exceeding the capabilities of the pilot, plane, or both.