Because they mostly all have terrible personalities and would find each other totally unbearable just like the rest of us do.

They also generally don't really want to date any sort of actual human that exists in the real world. They want to date a perfect parody of the opposite sex, incels are looking for someone who looks like Barbie (or whatever their idea of a perfect body type is, some go for a the petite almost childlike look after all) who wakes up looking like she just left the salon, who is totally subservient to all of his wants and needs, never speaks up unless it's to stroke his ego, a perfect cook and maid, an oversexed freak in the sheets, who will bear however many children his twisted ego wants to inflict on the world but never gain a pound or show any stretch marks, wrinkles, or grey hair

In short they don't want to date a real person, they want a real doll who does their laundry and squeezes out children.

And they're convinced that these mythical creatures exist out in the real world but that someone is conspiring to keep them from them, because obviously they're the perfect example of masculinity and why wouldn't these perfect females be flocking to them otherwise?

And I'm not certain exactly what sort of fictitious Superman feels are after, but the same overall sentiment applies.

Or else they're just deeply in the closet.