This is due to primarily to advances in technology (more reliable ovens, manufacture/availability of food molds) and ingredient availability (refined sugar). When removed the icing cooled quickly to form a hard, glossy [ice-like] covering.
At that time cake hoops--round molds for shaping cakes that were placed on flat baking trays--were popular. Many cakes made at this time still contained dried fruits (raisins, currants, citrons).
Gateau has wider applications in French, just as 'cake' does in English..can mean a savoury cake, a sweet or savoury tart, or a thin pancake." ---Oxford Companion to Food, Alan Davidson [Oxford University Press: Oxford] 1999 (p. Choux/ puff paste, sponge, French cremes, Gateau St. As time progressed, baking pans in various shapes and sizes, became readily available to the general public.
Torte is the German word for cake, with similar properties.
Gateau is generally used for fancy, but light or rich, often with fresh decoration, such as fresh fruit or whipped cream.
Whereas a cake may remain fresh for several days after baking or even improve with keeping, a gateau usually includes fresh decoration or ingredients that do not keep well, such as fresh fruit or whipped cream.
Although both terms can be used for savoury preparations (meat cakes or vegetable gateaux) their main use is for sweet baked goods.
Cakes can be large or small, plain of fancy, light or rich.