Firstly, it's important to understand that the art "industry" has a massive supply and demand problem - ie over supply and very little demand. This is in common with musicians, bands, authors etc.

On the one hand competing for very limited "shelf space" means that most artists never get into galleries etc.

The gallery owner is balancing multiple factors (cause they want to make a living selling art) and so public tastes etc come into play. They're also more likely to show "art their client base knows" to improve sales.

Museums have a somewhat different mandate, but often have more art than they can display. So they rotate works, create "themes" and so on. They need to keep their core market (repeat art museum visitors ??? ) coming back.

Of course pretty much all artists are "not represented" most of the time - that's fundamental to the supply demand problem.

Are pictures by old white men over-represented? Absolutely. Are they the ones who got opportunities 30 years ago, and have built both a body of work, and a fan-base of buyers? Equally yes. Are they the "safe choice" for dealers keeping the lights on? still yes.

Change will happen slowly. Buyers tastes change slower than artist creativity.

If you want to promote diversity in the art world, only one thing matters. Are you buying that art? Because if you're not buying, you're not sending a signal that matters. And (I say this as one who does buy art) a vanishingly small number of people buy any art at all.

You're right that things are different at private galleries. The majority of art in galleries representing artists decades into their career is not going to be by women. And the owners are going to have their say/taste, as are their clientele.

But, will that still be true in the coming decades? There is a pipeline to becoming an established artist, and what is the input to that, if not the art schools, collectives, and artist run centres? (I am not asking that rhetorically, I am genuinely curious)

Out of curiosity: what specifically leads you to make this claim? I don't necessarily doubt the claim, but your story up to this point could describe any budding artist trying to get recognized, as only a tiny of fraction of them do.