I'm not qualified to speak to why. I have suffered and many of my issues were due to a bad combination of burnout and 'I'm killing it' culture. Simply, admitting weakness in our field feels career ending and so the tendency is to push through burnout and depression. But, I wonder if the fear of admitting weakness is endemic of our culture of if it just a symptom of the disease.
In light of my past, I have started emailing my friends, telling them that I care about them, and letting them know that if shit looks bad, they can tell me. They don't need to kill it, or be ultra successful. They just need to be.
I've also wondered if something like that could become sort of a volunteer organization. Kind of a founders helping founders organization??