Since a dramatic peak in the 1980s, serial killers in the U.S. like Ted Bundy and Jeffrey Dahmer have been in decline for three decades. Experts have a few theories that can help explain why.
I'm not sure that you can safely label serial killers as incels per se. BTK was married, IIRC. Ted Bundy def. dated. John Gacy was a pedophile (more accurately a hebephile, but close enough).
Many of them were misogynistic for sure, although that's not necessarily a motive when you have serial killers that are gay or pedophiles (Gacy, Wayne Williams--believed to have been the Atlanta Child Murderer--and Dahmer). Incels seem to be much more likely to be spree or mass murderers; the idea of an incel where all women collectively share the blame seems to be a fairly new idea. And a lot of mass murderers aren't related to sex a all, like the people that have been trying to start racial holy wars by murdering non-white people.