It isn't just incompetence or life changes. If a therapist gets triggered in some way, that might be it. Boom. Mine saw that I was being traumatized somewhat by the process. All she could think of at that point was that she had failed terribly. Her own sense of self became the primary concern. I had to be eliminated. When I tried to have a real conversation about this a bit later she became hostile and refused to speak to me ever again. Have also read accounts of therapists suddenly waking up to some sort of enmeshment and freaking out and ending it.