I spent my twenties running long distance, but gave up four years ago. The frequent injuries were just too much. A bad injury once had me off training for four months. Going from feeling like a machine to someone who can't manage a jog in the space of an afternoon seriously messed with my emotional state.
I'm writing this on a recumbent bike. I've averaged ninety minutes a day for four years without injury. I've also read a ton of books on my kindle.
I'm a runner with depression. I track my mileage, diet and general mood very closely and have started to brace myself for a depressive periods after major races.
I need redundancy with coping mechanisms, and the OCD nature of distance running is potentially setting people up for a fragile system should an injury occur or low-mileage phase crop up.