1. they are shit
2. no one watches them (including women)
ask any woman if they watch female sports and 99% of them will say no they don't, and of course men don't want to watch that crap
This.
It's not muh misogyny, it's not some patriarchal conspiracy to keep women down.
Elite professional sport is TV entertainment. People want to see the hardest tackles, the biggest place kicks, the fastest cycle races, the longest drives, the batsman knocking it out of the park. It's a spectacle of mega performance. Sports heads WANT to pay to watch all that shit. That's where the money comes from.
All of these popular sports that people want to pay to watch, are sports that the top .1% of men are significantly better at than the top .1% of women. Success depends on speed and strength, and Women just simply aren't as strong, or as fast, and that is immediately obvious when you tune into TV sport. The women's game is just a slow, boring, low-stakes version of the men's game, so almost nobody is interested. No audience = no money = pay gap. No amount of shouting MISOGYNIST is going to change that.
[Notable exceptions seem to be tennis and beach volleyball, which are obviously just soft-core porn as they feature semi-naked 10/10 giga Staceys showing their ass under glaring tv lights and extreme camera close-ups and slo-mo replays. The fact that that even exists, is far FAR more misogynistic than the pay gap in football IMHO.

]
Idea:
Perhaps some brave empowered women athletes could put their heads together, and invent a new sport where male physiology is a disadvantage, and the women have a natural advantage. Start a competition for it, televise it, and if it's good sports heads will want to watch it. No yelling MISOGYNIST or PATRIARCHY required.