Besides which, they don’t have some of these units for all the nations yet.
For example, you mentioned a Light Tank set. At present, they only have light tanks for the US (Stuart), Russia (T-26) and Germany (Panzer II and Panzer 38t). Oh, and they will have some for Japan (Type 95) once the Expansion set gets here. For now, there is none for Britain, France or Italy. I suppose ANZAC could use British sculpts.
Well, I guess the Allied Supplement sets do come in UK Tan, ANZAC grey and France blue, plus the Axis Minors sets come in Italy brown so technically you could have light tanks for all nations. They would just be US and German equipment.
Perhaps in a couple of years or so when all the nations have supplement and expansion sets, HBG will think differently about those kind of sets.