I guess "Dobie" is too cutesy for a lot of people, me included. You don't see people calling GSDs "Sheppies" or Malinois "Mallies" .... cutesy doesn't fit some breeds, IMO.
ETA: If we're adding 'ie' to make breed names easier to roll off the tongue, why aren't Chows called Chowies, Great Danes aren't called Danies, Pugs aren't called Puggies?
I don't know. As I said, it's a peeve of mine.