Because they’re less of a spectacle. Men’s professional sports involve world-class athletes performing a level well beyond what their spectators could ever hope to attain.
Women’s professional sports generally involve competition at a level equivalent to high school boys or perhaps NCAA Div II/III men’s athletics. There are high school basketball teams in this country that could excel in the WNBA – if they weren’t excluded for being the wrong sex.
So you might as well ask why you’re not watching those high school boys play if the overall level of competition is similar.
Latest Answers