Students. Students make them that way. It’s no coincidence that most older teachers feel like they’ve checked out.

I did substitute teaching for about two years. I got to see a lot of my old teachers, Some classes were wonderful, a true joy to teach. Others, not so much. I can understand why some people, as you say, mentally check out. It’s a coping mechanism. They were not all the same people I remember. Maybe part of growing older. Maybe part of years of difficult students sucking out all the joy of teaching they had in them