Glossy toys go back a long way, Chris, as do playthings or small models - the original meaning of the word "toy" - with matte finishes. It often depended on the paints the maker had available.
I think the fact that the enamel paints used were hard-wearing and could stand up to playroom battles was a big factor in their use.
Many flats, on the other hand, were painted in colors that dried to a flat or semi-gloss finish.
The emergence of the toy soldier, painted in matte colors to more exacting standards of detail, what we would consider a miniature as opposed to a toy, began in earnest just before WWII. The British Model Soldier Society's group project to paint Britains' castings of Waterloo British infantry is a milestone on that road, as are the efforts of some toy soldier manufacturers, such as Jones and Warren, who aspired to produce something of better quality than other manufacturers made. Same goes for Comet/Authenticast in the late 30s and into the 40s. In Europe, you have the examples of Mme. Desfontaines, and Vertunni, and the Belgian gentleman who traded as MiM, but whose name escapes me, all departing in various degrees from the more toylike figures of CBG-Mignot, Heyde, Haffner, et al.
But all the while, toy soldiers were still mostly painted and sold in hard-wearing gloss enamels.
Prost!
Brad