I am not danieltillett, but I am familiar with the difference between doing research and supervising research. A tenure-track professor is expected to advise students who do research. The professor's involvement in the day-to-day of the research itself will vary depending on the student's experience, how large the professor's group is, and what the professor wants. While I do know of some professors who did almost an equal amount of day-to-day research work as their student on a project, that is rare, and such professors can typically only have one or two students at at a time.

Instead, a professor is usually spending more time supervising research. This is typically because a professor has multiple students, and as danieltillett explained, they already have many other time commitments. But this is also because the point of the entire process is for the students to become independent researchers. That is, the research supervision is teaching their students how to be researchers. In my experiences, professors in science and engineering tend towards being managers rather than being in the lab or at the keyboard.

I presume danieltillett made this distinction because there is a difference between supervising and doing the research.