It might be that they feel like they're "paying their own way". My paternal grandmother didn't want Medicare, at all. She said it was welfare (they were fairly well-off though not rich---my grandfather was a Captain). So because Medicare covers everybody whether they like it or not, she went and got the fanciest supplemental insurance she could find, that got billed before anything went to Medicare. So maybe in some small way that makes them feel better.It makes no sense for them to be paying for a Medicare supplement, with Medicaid in addition to their Medicare they don't pay anything anyway.