Perhaps the way and/or time in which your father was raised is causing this. Hell, society still tells men — actually most people — that depression and anxiety are signs of "weakness" and they should be something one can overcome if they really wanted to.
Attitudes have been changing and we've come pretty far but there will still be people out there who, without help, are unable to fully see what's really going on...

Depending on his age, along with his father's age, his expectations may arise from outmoded and outdated standards for what a "strong" person should be.
Is that a possibility?
His feelings of being "threatened" are in part why I suspect this.
It's not an excuse for his hurtful behavior. But it might be a reason. What do you think?