After Pope, in the beginning of Romanticism, people developed the idea that imagination rather than reason was a special form of knowledge and its best expression is through poetry. Therefore, poetry should not try to do the stuff that mere prose does: convey information or make arguments about ideas.
Robert HassMy suspicion is that once you have literacy in place, the readership has not changed very much.
Robert HassWhen Emily Dickinson's poems were published in the 1890s, they were a best-seller; the first book of her poems went through eleven editions of a print run of about 400. So the first print run out of Boston for a first book of poems was 400 for a country that had fifty million people in it. Now a first print run for a first book is maybe 2,000? So that's a five-time increase in the expectation of readership. Probably the audience is almost exactly the same size as it was in 1900, if you just took that one example.
Robert Hass