"Publish or perish."

The dirty secret of universities: the job of most faculty isn't to teach, it's to research and bring prestige to the university. In the sciences, research is a byproduct of bringing in money, so research grants are the most important part.

Thus, on top of those three classes (two at the university I live near) they're expected to put in full time work on their research.

From what I see, it's about a 60 hour average week in the social sciences. That dips to 35-40 in the summers.