There is zero benefit as a man to show vulnerable emotions or show any kind of weakness to anyone.
If they express their insecurities or daily worries to their wife/GF, then they're seen as weak and can't handle their own emotional baggage. Or they're seen as whiny or stressed out and that makes them stressed out. Men are expected to be rocks in relationships and women don't want to be in a long term relationship with someone who is not steady.
If at work, and seem overwhelmed all the time or emotional they are not leadership material and people won't want to work with them.
When they are with their guy friends and they are playfully ripping on each other, they have to play along and not take things personally or they'll be seen as a bitch/pussy.
Society is more sympathetic towards women in general. If a woman is feeling depressed, sad insecure, there will be an army of people ready to build her up and listen to her. Men are expected to build themselves up.
In no aspect of life is it benefitial for them to express their feelings as men. These are the expectations that have been placed on men by society.