He had everything, tenured job at a good school, kids, loving students, good pubs. Depression is a mental disease.
Thing is, his post doesn't suggest that he found anything about his job intrinsically rewarding. He lists things he enjoyed, and he clearly cared about his family in his own way (I know, I know, he still hurt them), but research, students, the profession - that wasn't a motivator, apparently. And I'm not saying it should have been - for some people, this is just going to be a job, no more. But we ask people to work as if this is their whole life.
Ditto. Research. Teaching. Service to the profession. His notes never mentions those things in any particular good light. They seem more like a drag and burden and problems to address. Take note, people.