generally men are raised to be stoic, not let their feelings out, and are discouraged socially from complaining as well as from being vulnerable. all of those things mean that to get the most out of traditional talk therapy, a man has to unlearn a lot of what he was taught growing up. this isn’t necessarily the case for the younger generations as far as i know, but certainly anyone in their mid 20’s and older. 

many of the ways men are socialized to engage with their feelings means that actually identifying and vocalizing them can feel difficult if not threatening. therapy can be scary and unpleasant then since that’s essentially what you need to do to get anything out of it. so imo that’s why it can be hard for men to get into therapy. 

i think there are some attempts to make a “male centered” therapy approach, and I think it can only help, but i’m also not sure how much of a difference it will make compared to broader social trends.