Some people have to cut ties entirely with those who want to interact with them because they are unable to keep firm boundaries.
I suspect that is what happened with my niece who doesn’t speak to her mother, and has not spoken to her for more than a decade. Her mother is not openly toxic and the two were super close until my niece turned 20. Sure, her mother is…”extra” (and she irritates her brother who is my DH) but there was no addictions or mental illness or severe outward problems.
My guess is that my niece, being young and learning her way along in life, wasn’t able to set the firm boundaries needed to continue to interact with her mother. Now so much time has elapsed in this mode she is embarrassed to change it.