Using Google's Ngram Viewer for the word fun gives an interesting graph.
Firstly we note a huge peak round about the time of the Spanish Armada. No surprises there as this is a search on English words. At this time fun could mean cheat, hoax or make a fool of - all very appropriate.
Then apart from a small peak of fun when King Charles I lost his head and another when King Charles II was crowned, the major feature is a huge peak of fun which seems to coincide roughly with the early days of the Industrial Revolution in the second half of the eighteenth century.
However, once it became clear that factories were one of the main consequences and the old ways were now no more than a bucolic fantasy, the fun seems to have rather seeped away, or at least trickled out of our literature.
Or maybe it was income tax, steam engines, Napoleon and hints of a recognizably modern world looming large on the far horizon.