There have always been incels- randy young men who can't get laid and don't see how it can possibly be their fault. Hamlet was an incel- or at least you can play him that way (the greatness of Hamlet is you can play him everywhichaway). Any poet who ever penned lines to his "cold" or "cruel" mistress was having an incel moment. Keats's La Belle Dame Sans Merci" is thoroughly incel. It's a phase. Most men grow through it.
All that's new is that the internet allows incels to flock.