It's a weird sort of psychological projection. Women think that since they are constantly surrounded by simps and cucks trying to fuck them, that must also be a normal experience for men, including you and everybody on this forum. So when you're facing living for another 70 years without ever getting laid or even having somebody who cares about you, they think you're just being a whiny bitch because all they have to compare that to is the occasional dry spell (which for them is 3 months in what they would consider to be an extreme worst-case scenario).
When they find out you have a serious disease which could end your life at a young age, it's a tragedy to them because in their imagination, you have a happy future in which you retire from thotting around in your 30s and settle down with some chick and have a family or whatever. Basically, they're imagining themselves having cancer because that seems plausible to them. Them being virgins for the rest of their life doesn't seem plausible to them because they've never not had access to sex, so they can't sympathize with that.