There's no artist in this world that doesn't enjoy the dream that if they have bad reviews now the story of Keats can redeem them in their fantasy or imagination in the future. I think Keats' poem 'Endymion' is a really difficult poem and I'm not surprised that a lot of people pulled it apart in a way.
Another cause of change one less noticeable but fundamental is the modern growth of population closely connected with scientific and medical discoveries. It is interesting that the United Nations has set up a special Commission to study this question.