I don't know if this would necessarily apply to all incels, but I think a lot of people who struggle with romance just want someone they can love who isn't a hedonist or who isn't otherwise unwell (think of all of those unstable women you've got fu.c.ked by, for example. It's apparently been difficult for you to find one that wasn't unstable). I don't know if I'll ever find a girl like the wonderful one I had, for instance.
It just seems far harder in contemporary life than how it would have been two centuries ago to find that person who "clicks." Perhaps one could blame this not only on the blatant, surface-level issue of faltering morals in modern society, where so many different levels of morality now co-exist without any clearly-dominant standard because of centuries of secularized culture, but also on the diversity of philosophies and other forms of thought that the "information age" has brought to all who can easily access the internet, so communities that were once far more homogeneous in their thinking have been split up, and with that, less people can truly relate with one another. I'm just yapping, however.