That's down to the (obvious) fact that job performance and working ethics is not equal but distributed among practitioners.

I think this is especially visible in software "engineering" with people joining the craft after a few weeks of boot camp. (think engineering vs programming)

However, we put doctors through an especially rigorous and long training and certification process to minimize the amount of unqualified practitioners.

Doctors are supposed to have a higher entry barrier than software developers. Does not mean that all of them are brilliant, of course.