Exactly. This seems to have been forgotten entirely, along with basic history about the fight for women's rights, of which separate facilities and services in certain circumstances (eg toilets, changing areas, dormitories, hospital wards, prisons, rape crisis centres, the right to same sex care for intimate medical services/checks etc) was one example. Evidence of a worryingly complacency that rights are set in stone and that changes are always "forward progress", it seems to me.
The Chesterton's Fence principle applies here. Before you remove something (like a fence that has been put in place, or a boundary) in the name of supposed "progress", it's sensible to understand why it was put up in the first place.
So to repeat this entirely pertinent question, why were separate facilities for women and girls fought for historically? Why are developing nations still fighting for them as a women's human rights issue? And yes, to pick up on what others have said, what is the advantage or benefit to WOMEN & GIRLS of mixed sex facilities exactly and the removal of single sex facilities? What is the benefit to the rest of society? Who does it benefit the most?