Mother Amy

So why is it that Uncle's are always referred to by their connection and their name (e.g. Uncle Chris)? Why no Father Chris or Gramps Roger? Maybe I heard some Granna Linda's, but that's it. Not that I'm complaining about being remembered, or anything, but seriously.

It's always Uncle Joe, or Uncle Scott, or Uncle Something-or-Another. What is it about Uncle's that requires an extra level of categorization?