I hate to go the dark route, but maybe they don't want to be proven wrong. Maybe the prospect of access to sex for them (at least, for some of them), is so remote, and the messages promoting sex as pleasurable and desirable so strong, that they in fact take comfort in the notion that maybe the juice isn't worth the squeeze.

It's like with MGTOW. Everyone is always like "why do those guys keep bitching about women if they've gone their own way?" Well, it's not necessarily an easy choice to make to Gotow...of course someone who is going against the grain of what society and friends and family and media pound into your head day in and day out as the end all be all of life (love, relationships, sex, etc.) is going to want to restate and find affirmation for their justification. You only get one life. Going against the grain is fucking scary.

Fact is, there is no concrete reality of what your experience will be with women, or with people. Your mileage may vary, and there's no way to predict what those specific instances will be either way.

So tldr

Many (most?) incels are incentivized to voice the opinion that women are terrible because there is no reasonable hope of ever being with one.