To those who see themselves as teachers first and last, this question may seem unnecessary. But many grad students and faculty at research universities may feel that their vocation lies elsewhere. Even if the instructor saw no personal benefits from working with students at a basic level, helping people to reach otherwise overwhelming goals would be a worthwhile achievement.
Teaching is our job.
Students, their families, and the public all expect that whatever else goes on at a university, teaching stands at the center. This is why they pay fees and make donations, which go toward paying instructors and staff. Teaching develops relationships. Some of the most profound and long-lasting friendships are between instructors and students. Teaching produces future researchers.