This is actually an issue I have been very intrigued with lately. And, its probably too big to get in any one "take". But the gist of my intrigue is as follows....
For years and years and years we have considered there were 3 main sports markets in the US, and those sports markets were predominantly made up of men. MLB, NFL, NBA.
The first part of the question is... Why men? Are men genetically predisposed to be fans of things more than women? Taylor Swift and Kate Spade and Stanley cups would beg to differ. Are men more drawn to sports because they have always been exposed to them culturally from dad's/grandpas/uncles etc? Do men tend to enjoy sports more because they played them growing up?
I admit I do not know, but to me it stands to reason it is some form of the last two concepts. Well, starting in the 70's when title nines and thing started to come around, now you have women starting to compete in athletics in much higher numbers. If we are being honest, at first it was painful because, overall, these were NOT competitive areas as they were brand new. Basketball was slow and ugly. Softball was an underhand pitch bastard knock off of baseball. Etc. Over the last 50 year, however, the womens sports have become much more mainstream the the quality and competitiveness across the board has improved. More importantly, each year that goes by you have more and more women who grew up and PLAYED high school/college basketball. Now they are much more a part of the sports '"fan" equation.
Stands to reason that marketing toward women, especially in areas like basketball, volleyball, etc could likely double your potential fan base.
That said, they can only follow the things that are broadcast to them. So, again, if it is only NBA, NFL, MLB, etc, that is the only thing anybody can easily fan up and follow. Sort of a chicken and egg thing, which comes first? I don't know for sure, but I'm almost certain that the MLB is dying because those games are too many and too boring, and in its stead a womens pro volleyball match could very possibly draw more eyes more easily in the current world.
Who knows?