Because some men use women platonically as well as sexually
I think there's something in this, though I also have several longterm, unproblematic friendships with men and am happily married to a good egg.
But I had what I thought was a good, more recent friendship with someone I got to know through my young DS's friendship group (divorced father of one of his friends, child spent weekends with him, and as both children are onlies and DH works away a lot, we spent quite a bit of time together at weekends as a result, doing stuff with the children). We confided in one another a fair bit, and I was really pleased I'd found a new friend, as we'd moved house not long before and I was actively on the lookout for new people. No sexual attraction, plus I'm at the extremely plain end of the spectrum of looks.
And then he just stopped getting in touch. I kept contacting him for a while, in the usual way, and at one point when I hadn't heard from him in a couple of months, asked him if I'd done something to offend him. No, he's 'just been busy'.
With hindsight, it was clearly the platonic equivalent of a situationship as far as he was concerned. I'm a confident person who doesn't generally struggle with friendships, but I was really hurt, and felt like an idiot for thinking it was a meaningful friendship, when he appears to have deleted two years from his memory without difficulty. I think I was a useful source of female company and conversation during a lonely spell after his divorce, and then there was no longer a role for me once he was feeling better, and our children no longer played together much.
I can only conclude that I was platonically 'used', and am a sadder and wiser woman as a result.