It only takes one time: a woman who sees a man as less than for admitting his weakness makes him never talk about that stuff around women again.

Unfortunately, there are many women who react this way, so the cycle continues. I don't necessarily blame women for this, it's more about the social expectations for men, the moment they violate that expectation and are "punished" for it, they follow it to the letter, because they then know what happens if they don't.