The idea that classical composers (before about Liszt) were the "pop music" of their day is uninformed. Consider 1) the size of the venues that Mozart or Haydn's secular music was performed in, and 2) the fact that the bulk of the population was peasantry who wouldn't be admitted to such venues in a time of strict class distinctions.

Outside church settings, classical music of the Baroque, Classical and early Romantic eras was for the elites, and the masses had their own musics. This only changed gradually over the 19th century.

It's also weird to still be hung up on atonality in the contemporary classical world, when the pop-music world has for decades now had acts like Merzbow that are often farther out into noise.