I think it's possible people overstate their T's flaws and/or underrepresent their attachment to said T, and maybe that's part of what's going on. I know I've done it as a way of distancing myself from the potential hurts of an intimate relationship.

I also think it's possible to use therapy for a purposes that might seem inexplicable from the outside. Maybe one enjoys or benefits from an adversarial relationship, finds in the therapist a sparring partner, wants nothing more than a dumping ground to vent, or simply doesn't want even the possibility of attachment (and so stays with a therapist they dislike because attachment won't ever be an issue) Those seem like legitimate, if somewhat unconventional, uses for therapy.

I can imagine some unhealthy reasons, too. Maybe the client doesn't know how to be anything but martyred--I certainly know people like that--or doesn't feel they deserve a warmer relationship. Maybe the client is just so stuck they don't have the agency to leave. Maybe an unethical therapist has robbed them of their agency.

Anyway, it's an interesting question.