I Wish Tomy Would...!?

...and utilize Diesel for a three-pack, as he does appear prominently in the show and there isn't currently a TOMY Diesel in production for that need

This quote brings up and interesting question about how Tomy (or Mattel for that matter) decides what to produce. They obviously aren’t in the stage of “make ‘em all” anymore but sometimes the omissions are strange. I’m sure character popularity and prominence play a role but I wonder if market saturation plays a part. Diesel, for example, is a prominent character but older issues of him are still fairly easy to find. Maybe his popularity is weak in Asia as compared to say, North America or Europe?

I’ve wondered the same thing with “real world” Plarail items too. Why is there so little separate rolling stock but certain trains and locomotives are produced in numerous variations every few years?