It don't think it it ego as much as it is professors prioritizing what they need to do. At a minimum, their job requires that they (1) publish, (2) teach, (3) win grants to bring in money for the school. Even for professors who are tenured, they still need to fulfill these requirements. This doesn't even include meeting with students, advising doctoral candidates, reviewing for journals they are published in (i.e. once you pub in a journal you become a reviewer for them), writing personal books on topics, or organizing school/student events.
Professors, in their defense, have a hell of a lot going on. Ego may be the reason why some of them don't contribute, but I think a lot of it has to do with simply being busy. Being a professors (especially a tenure-track professor) is a full time, 7 day a week job.