This topic is complex. I've been on the case talking about breast cancer in men and the reluctance of the "pink charities" to be more publicly active in engaging with men for 12 years now. With mixed success I might add.
Big issues for very many men are the stigma of a diagnosis and their reception when they go through treatment (pink gowns, gender-specific forms, etc). As well, there's often reluctance by men to properly follow up on health issues, particularly BC symptoms, and, upon diagnosis, the issues attached to coming out with what is mostly perceived to be a woman's disease. Two years after my breast cancer diagnosis, I was treated for prostate cancer, so I've trodden two cancer paths. I've also seen the difference between fundraising for this disease compared to breast cancer. I believe the latter draws in ten times more dollars for research than the former.
Here's an article I wrote a couple of years ago:
https://preventcancer.org/article/male-breast-cancer-stigma/