Perhaps you might be conflating the two sayings "go figure" and "it figures"? Is there some distinction to be had there?

I don't know if this really helps, but just for this example alone I would interpret "waiting on your mother" to mean the rest of the family is ready to depart for somewhere and she's holding up the group while "waiting for your mother" would mean she has not yet arrived where the others are located. (I'm from Michigan, for what it's worth.)