Correct. Professors bring in money by teaching, for which they aren't paid any extra, and grants, which often they receive a small monetary incentive, i.e., su

Correct. Professors bring in money by teaching, for which they aren't paid any extra, and grants, which often they receive a small monetary incentive, i.e., summer salary of about $10-20K per year for a professor making $100K. It is hard to get much more than that because of caps on grants, so for professors to get paid more by grants the maximum size of a grant from NSF/DoD/etc. would need to be a lot bigger. A question I have is "Why aren't professors who teach larger and more popular classes paid more for taking on the additional students?" My deep learning classes fill up to the maximum size allowed (50). I could scale it even higher, although finding class space would be hard, but if I do that my university has no explicit mechanism to reward me for doing that. If you teach more people, you would think that you would make more money.