Why dont many girls like prog?

Well in mainstream examples:

That started to change in the 1970s when you had artists like the Runaways or Siouxsie Sioux knocking down barriers, but it hasn't changed as much or as rapidly as you might think - even in much more recent years you had bands like Kittie where "they're a metal band but they're all women!" was considered unusual enough to be a marketing point, rather than being utterly unremarkable, and even today genres there's an ugly tendency to write off genres which are directed at a primarily female audience as having less artistic credibility.

In the case of prog, it arose when that gender divide was very much a thing, and it's kind of inherited that a little. Prog bands were mostly men, record companies mostly marketed prog to men and boys, and soon you get a self-fulfilling prophecy - a boys' club which by its nature feels far less welcoming to women than an arena where women are more visible both as artists and as audience members.

I think a lot of us, whatever our gender, wouldn't feel so comfortable at a gig if we felt like we were the odd audience member out - if everyone else you can see is a different gender than you, or a different race, or much older or younger than you, or dresses in a particular style, it can feel pretty isolating. That's not conducive to relaxing and enjoying the concert. Likewise, when I grew up if a boy admitted to liking particular types of pop music at school, he'd get a heap of absolutely appalling homophobic bullying because he liked "girls' stuff", and girls who liked rock music got a similar outsider status - peer pressure is a powerful thing.

How to change it? Support women making good prog, just as you'd promote men who made good prog, don't pass on a group just because their vocalist is a woman, and make concerts welcoming to women by ensuring that men who creep on female audience members get thrown out just as they would if they made the men in the audience uncomfortable. It's the same in pretty much any subculture that's trying to rebalance itself in a similar way.