Another thought, perhaps, is that the advent of recording technologies took music out of popular control in a lot of ways. The ability to record music means you have to find music worth recording--so suddenly public music is performed by the musically gifted, rather than being a communal activity. Before the gramophone, poetry was a matter for poets, but music was something everybody did; the intrusion on poetry's market share may be more related to the fact that music became professional than to the fact that it was more widely available in certain forms.