Why are men only spaces met with indifference or backlash ? Atleast until they start allowing women in ?

As the title states, I’ve noticed that there are tons of women-only spaces and resources, but rarely have I come across similar groups or resources for men. On the few occasions where men-only spaces do exist, like shelters or charities, they often face backlash or are accused of being sexist institutions.

I personally want to see more men-only spaces, but I’ve noticed a troubling trend where other men seem indifferent to this issue. Many will even go so far as to say they don’t care for men-only spaces or that it’s okay for women to be included in these spaces.

Why is this the case? If you don’t personally feel the need for men-only spaces, that’s fine, but why actively disenfranchise the men who do? Everyone should have the right to safe and supportive spaces tailored to their needs, so why is it so controversial when men seek the same?

I’m curious to hear what others think about this, particularly why so many men seem indifferent to or even dismissive of the idea.

Edit: just FYI I’m looking for responses from Men only.