In 1950 there was a shortage of men and women were expected and somewhat required to marry off meaning it was feasible for an average to even below average man to get a woman, in the 60s and early 70s there had been an entirely new generation that had come of age and perversions such as the sexual revolution/women's liberation and even more female employment were in full swing, things were brutal but not as bad as they would become as some families were able to insulate their daughters from that and force them to settle for average men, by the late 90s even most of the elderly had grown up in a world where women were able to survive on their own and the older men grew up in a time of female abundance and thus would not be able to relate to the struggles of the modern incel. In all honesty I think the 90s may have been the most brutal time for incels as there were more than there were previously, nobody to relate to their struggles, and acceptance of sexual deviancy had already become normalized. Everything since then has been just more of the same but with continually decreasing quality of women and increased hypergamy.
