bodybuilding contests are about maximizing the body's physical/muscular potential. that is being lean, and demonstrating how well you've shaped every muscle on the body. It's a real art to itself to get a particular set of muscles to highlight every detail, etc. It's the human version of a dog show, or cattle/farm shows. It's definitely not on beautiful looks, but physical potential.
beauty contests...I really don't know...they seem to be dependent on makeup, hair, surgical treatment, and with very subjective western standards. I think the idea of beauty contests is outdated.
They are both
beauty contests....one is of male beauty and the other is of female beauty.
Looking muscular is a stereotypical male characteristic of male beauty.
Looking curvy and lean with smooth skin etc...are stereotypical female characteristics,
Which is why I said removing the beauty rounds off the pageant is as ridiculous as a body building contest with all competitors fully clothed.
(yes, there are female body builders...that's an exception)