Imagine being a lawyer, and people...liking you. That's what law professors feel like. They get all the glory associated with the law—Moses, pillars, unsmiling portraits of jurists in front of Federal Reporters—without the suggestion of unethical behavior. When they're hard on students, it's not to win, but to make them better advocates. They don't need to play dirty or take advantage of the system.
It would be hard to believe an opposing lawyer telling you he was making you a better advocate when he just sent a dump truck full of erroneous, though discoverable, evidence for you to sift through (especially if there was a dirty needle in that heap just ready to prick you). Plus at the end of the semester, law professors get a customary round of applause from their students. If jurors and the audience could let lawyers know how they felt about them at the end of their closing arguments, it might be like an episode of Springer. Now you know why the benches and chairs are bolted to the courtroom floor.