The simple answer is that taxonomy is not cut-and-dried and there is eternal warfare between the "lumpers" and the "splitters".
So while dogs could be considered a non-geographical "ring species" by the "rules" (which in reality are treated more like guidelines if you ask me) it isn't very likely that anyone will propose that the dog species is split, let alone getting it past the committees that decide such things.
To point to just one example working the other way, the European White-headed Duck (Oxyura leucocophala - mainly found in Spain) and the North Americal Ruddy Duck (Oxyura jamaicensis - introduced into Britain), are considered different species. That hasn't stopped the British Ruddies hopping over to Spain and having their wicked way with the Senoritas, to the point where it is considered a significant threat to the already-endangered White-headed duck species.