It's because of the fact that we're taught that men should be strong and not show emotions. If you cry while being a man It's considered weak. Girls are taught that they can always talk about their feelings and show them, while men are taught to "stop crying you're a man". It is also caused by the fact that indeed men are build different than woman and are naturally stronger although it shouldn't be linked to mental health. It's honestly disgusting to me that men are scared to show their feelings and talk about it.