Schools don't teach this stuff and many people just don't know. In a school you automatically get the physical and social aspects (PE classes and forced collaborative projects, with a timetable you had no say in) but after graduation a lot of people didn't know they needed to expend effort to keep doing it. The first year I was working I didn't know I needed to actively exercise, or actively seek out social activities beyond just immediate colleagues.

Fortunately I fixed that early in my career. I'm sure plenty of others still haven't.