In my experience it's the prevalent sex stereotyping that stops boys doing ballet.
Dd's school have a lunchtime ballet class. There were several boys try to sign up, but their parents wouldn't allow it. Dd is a huge Steven McRae fan and was puzzled- at the time (age 6), she honestly thought ballet was for boys
I once had a colleague, with a postgraduate degree in science. We were chatting about our children's hobbies, and talking about dance (she was a dancer/gymnast). Her little girl was doing ballet, modern, tap, as usual. I asked what classes her boy took.
She was absolutely horrified "oh no, he does football with his dad".
Older dd does gymnastics in a large sports centre. The coaches get very frustrated as the parents drop their dd's off on the way to taking their sons to football. They are desperate for boys, but just can't get them through the door.