The general concept underlying the "incel" insult is that women have the power to decide a man's value be denying sex to men they deem low value.

At the same time, women need to "safe face", and pretend they are not sluts. The insult involves women NOT having sex, therefore preserves the false narrative that women are chaste, non-sexual, and are not using sex to manipulate and gain power over men... its the perfect feminists eat-your-cake-and-have-it-too.