Professors do three or more jobs but at the end of the day they are directly judged on their lab’s research output and both directly and directly on how much grant money they bring in. The professor’s lab’s research depends not just on the professor’s ability to do research but (arguably more) on their ability to manage, attract good grad students (Graduate students are the labor in academic science and engineering), and bring in enough money to keep the lab well funded. The professor’s name and reputation goes on everything that comes out of the lab, so there is incentive to have the biggest lab you can without compromising quality (and possibly there’s even a Pareto-front where you compromise quality a little to
Therefore, the most successful professors are usually the ones who are the best grant writers and managers. A professor’s success is not entirely decoupled from their ability to do research because People who have done a thing should be in charge of a thing.
The more a field depends on large labs and expensive equipment, the less professors do actual research because they need to recruit and fund graduate students. Science has become more capital and labor intensive over time