I've been physically disabled from birth. I don't want to get too into detail, but suffice it to say it makes movement, especially vigorous movement severely painful. I am unable to sex because of this. Moreso, even just getting a hug can be pain :(
I've met other Incels online and a lot of them have similar issues. One girl I spoke to said that she couldn't attract men because of various birth defects and how men perceived that. She would even be extremely forward with men asking them to have sex or trying to seduce them and they outright told her that it was her conditions that made them say no.
A third person, an American POC I know, has never been able to get a date. I personally think he's attractive, but that's me. He recounted to me a time where he was rejected and the person made it clear it was because of his ethnicity. Mostly racism here, but still an incel due to people being racist pieces of shit.
I guess the point I'm trying to make is that oftentimes Incels aren't just bitter misogynists living mommy's basement, but are victims of forces beyond their control such as disability or racism. Generally I feel there is a bit of Ableism in using Incel as an insult. I saw it as a non problematic insult sugggestion the other day and thought I'd give my two cents. Thanks.