In my experience a lot of those jobs are handled by more specific people I wouldn't exactly call just plumbers. There's far more to it than people realize for sure but it's still not rocket science.
Probably them choosing to do the thing. Someone doing a PhD might be hoping to land a good job later on and be able to through that pay off the debt. Or they want to pursue their passion, even if it means debt. It's a decision to go for those. Could've gone to trade school.
No but it just includes it, as part of it, not as the ultimate part