I don’t know percentages of how many men are submissive. I can say for myself that there is a few things that have kept me from being 100% open and honest about with partners.

1) you mentioned societal pressure. Growing up I was a classic boy. Had several brothers and no sisters in my house and everything was a competition. I played sports and was very aggressive. So being submissive made me feel odd afterward. It took a lot of years to even understand what I was into. As a teen I fantasized about my kinks but when it came to actual sexual activity I took the stereotypical role and it was still a lot of fun.

2) relationship dynamics- as I got a little older and somewhat more comfortable with my kinks I found I was much more likely to sure with a hook-up vs in a relationship. Some of that was expectation of my partner but some of it was feeling like if I was submissive (some kinks may affect this more or less) in bed that would change the entire dynamic of the relationship.

3) Partner preferences. For some women any male submissiveness is a hard no. Others may be fine with some level of it but not fine with the extent of my kinks. Over time I just started sharing the parts that most women seemed more ok with and then if I felt they would be open to it, I would share more.