Why does family sharing prevent one ID from having multiple families, it's not that uncommon for one person to have multiple families they're involved in.

I was very disturbed to discover that Apple's family sharing only has the capacity for one family per ID. People nowadays are part of multiple families; whether through marriage or divorce, and those families don't necessarily want all their purchases shared with the other people. Why can't they just allow people to have multiple families, I understand there might be some complications with payment methods, but you could just let them choose which organizer they want to ask permission from, just like they would in a real family.