There is something great about being amazed with what the human body can do. Watching the NBA and the NFL includes some of that amazement, sure.
But I've had a really, really great time watching something like college baseball. And the players are good, but clearly not the best.
Women's tennis sometimes really delivers entertainment. But everybody serious knows that Serena Williams couldn't win a set off of any man in the top 500. She knows that's true.
Nobody has to like WNBA, of course. I don't watch it hardly at all. But the whole "they couldn't beat a HS team" schtick is an incomplete explanation for why it isn't more popular, IMO.