Somehow, we've conflated character and loyalty (which are important) with the willingness to suffer needlessly in the name of subordination and whatever the fuck "team player" means.
The brogrammer culture and unnecessary long hours of Corporate America are all about testing people based on their decline curves, not peak performance. It's competing to suffer rather than competing to excel. Who is the first to crack? Fire him. Who is the last to break? Promote him. It's ridiculous and of course it's going to lead to an "epidemic" of mental illness.
In the corporate world, we promote based on participation in shared suffering (i.e. who stays until 1:30am to meet an arbitrary deadline) rather than talent, and we kick people when they're down, which is why it's impossible for someone to get back into the career game after even a short time outside of it (maternity, illness, depression). Of course we're going to have our best people dropping like flies.
Depression and anxiety disorders have always existed, but they don't need to be this common. I wouldn't be surprised to learn that at least half of the problem is caused by social and economic forces. These problems are biological at root, but social factors tend to modulate the severity that people experience.
Mark Suster deserves major props for speaking out about this. I've criticized him in the past, but I'm starting to like the guy.