They see movies and increasingly more girls on social media doing this. They lack friends and social experiences that show them anything different. They get caught in this circle of hate where they're hopelessly alone and think everyone is having sex but them, especially the people that bullied and rejected them.
It sucks not having sex and relationships in your youth, and it's normal to feel sad and alienated about it. But, the reality is there's lots of people that are lonely and suck at relationships out there.
I've been wrapped up in internet friendships and shit all my life, only just recently investing a bit in mainstream social media like IG and LinkedIn for the sake of keeping in touch with family, work, and classmates. The more I speak with and observe these "fucks on the regular" kind of people, the more obvious their lack of happiness is. Sure, they're occupied and have plans constantly, but those usually only serve to foster the relationships they then utilize for parties and cafe trips.
As much as these idiots keep pulling on "society" and "culture", I feel it has a play in it. You're considered inferior to a person studying the same as you, regardless of grades, because you're not spending half your week working to afford the apartment downtown with all the cool kids, who spend the remaining time partying and going 'woo!' on Snapchat. They most likely don't have hobbies nor do they invest in communities or regularly articulate themselves online. They do however fuck with people, which is the ultimate goal of most youth and as such are validated.
I used to hang out on this semi-normie forum as a teen and recently revisited it. It has a lot of considerate and thoughtful girls on it, but every single week ended up with blog posts about "did the guy i've fucked 3 times actually care about me? I hope I'm not pregnant. I really want a real boyfriend. Oh look, I can ride this dude's dick again!". To me, it really just is going between games, voice calls, and posting a bit on forums, but in a way less productive manner outside in real life, that is only validated by what we've come to consider positive behavior.
Incels speak out in a hateful way on an issue I think all people between 15-30 experience share, except society deems them losers for underlining what everyone else has; romance and sex, while from what I've seen, these people lack depth and interests developed from being a considerate and engaging individual. Every step through life has rewarded you for kissing and fucking. Whether by being the cool dude or by being patted on the back by your parents. "Even if you fuck up, you can still start a family".
The closest to an incel I've known in recent times basically said fuck it, got into learning Chinese, poetry, visual novels and joined a book club. You don't think it'd strike him 50 times harder meeting someone there with genuine mutual interests, as opposed to whoever he'd have to pretend to like solely for her looks? I recently revisited Tinder as well to see how it has changed, and it's almost painful to see someone who never developed as the platform did. Pics of their abs, yoga pants an inch above their genitals, on all four in their apartment. Then you swipe left and see someone with hobbies, interests, and the ability to entertain herself.
I don't think we need to sit down incels and shame them; more so have some kind of homeroom included in mid-teen education about life in general. Jobs, taxes, feelings, socializing. Maybe if these idiots saw that you can have other things on your mind than girls, such as actually enjoying life, they'd maybe seek to do so themselves, as well as seek someone who did it as well. Having developed hobbies of my own, even the idea of some bimbo with "wanderlust, music, netflix (heart)" in her bio approaching me would seem insulting.