Universities are institutions of research, that also happen to teach. To many faculties, students are a necessary evil to fund research. In order to teach students about their research, they have to go through three years of basics, not-so-basics, and then maybe some - to the professor - dull, repetitive, been-there-a-hundred-times preliminaries to their work.
The teaching many of them enjoy is their departmental or faculty seminars. And as a senior undergrad, those were the sessions I enjoyed attending the most. No surprises there. They were talking about the subjects they enjoyed the most.
Now - I'd argue that a professor should be bringing in revenue - either by teaching a popular set of courses that are relevant for students - or by bringing in research dollars. But then that's somewhat missing the point - universities should be exploring areas that industry doesn't yet understand and therefore doesn't want to fund... it's a quandary for sure!