Mmm… I can’t speak for the OP, of course, but family interpersonal relationships are usually embedded in a twisted nexus of cognitive-dissonance contradictions.
It’s quite possible that they have picked up on that obvious fact, but refuse to accept it-- or perhaps it’s more accurate to say refuse to accommodate it.
If they have the popular traditional “family values” mindset, they may well see an alienated or hostile relation as a “Scrooge” who is crying out for intervention, and regard attempts to avoid family gatherings as an invitation to step up intrusive persuasion.
Put another way, they may harbor a generally-approved “We Are Family!” social fantasy in which certain gung-ho family members are “enforcers”: would-be Good Shepherds who will seek out and reel in stray black sheep with a vengeance.
They insist upon the reluctant relative participating on “principle”, willy-nilly, in order to fufill their abiding group fantasy (or “ideal”) of family life-- i.e., no “out-grouping” allowed. Crazy, ain’t it?