This is a valid point, but due to that they're often-used, and that anything considered a "music" is loaded only when being used and can only have one loaded at a time (whereas sound effects are loaded in advance and kept in memory, and can be any number of them in memory), treating them as sound effects works much better from a coding point of view.
With that being said - on the Config Menu there are options to turn them off altogether, seperately from turning off regular sounds or musics.