People do sometimes get behind stuff from a nationalism point of view if their team is doing well in a tournament, for example. But if the quality is poor, it doesn't last.
There seemed to be a lot of interest in the last women's World Cup in England, for example. But I only found out yesterday that England are playing Spain in the Euros final (a rematch of the WC final) tomorrow. I didn't even know a tournament was taking place!
The biggest issue with women's versions of traditionally male sports is the lack of investment and opportunity. My background is combat sports, where all but a handful of women competing 'professionally' don't train full time and have a 'real' job that pays their bills.
Most people who support a football team support the men's version of that team. Most people who go to watch a game, or watch on TV, are doing so because they support the team, or they know it will be a great game of football. What incentive do those people have to invest time money into a much worse version of that game?
That doesn't make them sexist. I won't go to the cinema to watch a crap movie if there's a Scorcese film in the next screen.
That does unfortunately leave women's sport in a catch-22...but ultimately if there is a demand for it, the money will be found and the level will improve.