IMO, women like men who are mature and self-assured. Agreed they don't find much husband-material in someone who sleeps in their parent's and plays video games and participates in Incel forums all day.
As for the Halloween-theory, I disagree. A more likely cause is the Internet and, later, smartphones. Anyone can access free porn. For the stupid and lazy like Incels, this often means they think all women are easy. Stupid, yes, but Incels are stupid, immature and should be kicked out of their parent's homes so they can grow up.