Why did the woman fail to have lunch with the man?

M: Hi, Janet, where were you at lunch time? I was saving a seat for you in the cafeteria.
W: Oh, sorry to miss you. But my thirst for knowledge was greater than my pains of hunger.
M: I never had that problem. So where were you?
W: My political science class ran overtime.
M: That’s been happening quite a bit lately, hasn’t it?
W: I guess so. Actually, what happens is that a lot of us hang around for a while after class to talk with our professor and ask him questions.
M: Who is this twentieth century Socrates?
W: Professor Howl.
M: No wonder.
W: Have you ever heard of him?
M: Mm, he does have a good reputation in the political science department and I heard many people speak highly of him.
W: And a well deserved one. The same students who fall asleep in discussion groups and seminars fight for front-row seats in his lectures.
M: Oh, no. I hope this isn’t catching.
W: You can joke. But it’s great to have a professor who’s not only interesting but prepared to give up time for students.
M: I know. They are a rare breed. Maybe I should sit in on his class some time. Do you think he’d care?
W: Not at all. Lots of students bring their friends, and he says he feels flattered.