The reason for this is because unlike Townies & the other NPC groups, new Downtownies are not assembled by playing mix-n-match with CAS content & are instead created from a very small set of hard-coded templates, meaning that the only way for a player to have truly unique looking Downtownies was to create them by had in CAS & make them into Downtownies via a mod. (Usually one of Inge's teleporters.) While this certainly worked, it really sucked for folks (like me) who rather enjoy the element of surprise that true random generation allowed for.
Well, kiss those hard-coded template days goodbye!
Aaroneous has just released a long overdue mod that squelches those blasted *hidden* templates & allows auto-generated Downtownies to be created that same way normal Townies are, finally ending the terrible "Curse of the Triplets" once & for all!
It's on his Sim Manipulator site & can be found under the Odds & Ends section in the download area.
I included the direct link when I filled out this form/post, however last I checked, you have to register to download anything there, so it is possible that the direct link won't work for non-register folks. In that case, here is the link to the main page http://simmanipulator.forumotion.com/