The median MLB salary is just under $4 million, and the NBA is about $3 million. The players choose to play sports professional, which was often a dream from childhood. There's probably quite a few bored office workers who wish they could have played in the pros. Sports also employs people working at arenas and in the media, and boosts sales near the arena.
There was a story a couple years ago about a professional tennis player, Noah Rubin, who was ranked in the top 200, and how it was difficult for a player outside the top 100 to make a living traveling around playing at smaller tournaments without being able to afford a coach or trainer. Noah started playing when he was 4 years old. It was his dream to play in grand slams and be successful, like hundreds of other top 1000 men and women's tennis players. There is no rich owner taking advantage of them.
The WNBA doesn't make the kind of money to enrich owners, but the professional women do want to play basketball for their careers. It's a bit lazy to just dismiss all of professional sports as enriching a few owners and top athletes.