Resentment comes easy to incels. If they are doing many sessions they are likely to fantasize about their relationship with the Domina escalating and when it becomes clear that it is not happening can turn.

Financial strain could play a role in some cases. If they are spending more than they afford on sessions and there is no sign that they are going to get what they really want they are likely to start feeling that they've been exploited. Something like a polite suggestion that they try a longer than usual session might trigger them.