Plus a lot of people get major grief from others if they mention wanting to cut jerks out of their lives. “They’re family!” “You only get one father/mother/etc!” “What if so-and-so died and you’d never made peace, you’d carry that guilt for life!” Even similarly-treated family members can be the ones laying on the guilt trips.
I’ve often mentioned my abusive, bipolar father-in-law. My husband never cut him off years ago because he wouldn’t get to see his mother. Well, years later he begins to think of it as ‘well, mom never stood up for us that much when us kids were abused’ and he learned of a few incidents where she was going to file divorce but got talked out of it by him and/or changed her mind. (She came from a wealthy family who stayed in touch with her and would have supported her, so that wasn’t it.) So losing touch with his mom has become less important to him now.
Then we have the other siblings. Some of them don’t want to lose touch with their mom. Some seem to have a fair amount of “Stockholm syndrome”, in which they seem to have sided with their dad because he had the power in the family all through their childhood; they learned their mom wouldn’t really be that effective in helping them avoid abuse, so they desperately tried to stay on their dad’s good side against anyone else. I’ve seen that even today - blaming their mom for things that probably aren’t her fault, or dishing dirt to their father on their siblings rather than risk cross-examination by him on why they aren’t measuring up to his standards.
We’ve become estranged from my husband’s father, but as a result, since he and their mother must be invited to family holidays, this means we haven’t gotten together with his siblings for quite a while. My husband is planning on re-establishing relations around his mom’s birthday, with (hopefully) a no tolerance for BS policy around that time. I’m half-tempted to just not go since his father has little love for or understanding of me, but on the other hand I feel compelled to be “backup”/moral support for my husband.