A professor heads the research group. They are very busy. They have one or two specialty courses a year that they give. Most of the stuff they do is manage all the researchers in their research group, the post docs, the university lectures and all the other tenured staff.
I know some of you call everyone that stands in front of a class beyond high school a 'professor', but professors are the CEO's of the academic world. How do I know? How do you not know? A big physics forum pins 'staff emeritus', 'science advisor' and 'education advisor' next to your name but you have no experience in the academic world?
Yes, I admit it depends a lot on what type of lab is run. But sometimes a professor has 50 people working under him, with more than half of them having doctorates. And yes, in business or academics, not everyone gets to boss around 50 other people.
And if you have that many people working for you, you already have a full-time job just keeping up with what everyone is doing.
I don't see how you can stand in the lecture hall every morning, do measurements yourself in the lab every afternoon, and help read every relevant publication and get all the post-docs and tenured researchers unstuck the moment they can't figure it out themselves, and make sure that the PhD candidates that are managed by your staff actually live up to the standards. Because that last thing is the main thing that differentiates a professor from all other academic staff.