I think we might be arguing two different points. I certainly don't doubt there are more fantasy works in produced today than there were forty years ago, but there were plenty of recent fantasy books for me to read in the late 80s and early 90s. I'm talking books that were published from 1970 or later.
Books by Roger Zelazny, Mercedes Lackey, Stephen Donaldson, Raymond Fiest, Robert Jordan, Marion Zimmerman Bradley (unfortunately), Terry Brooks, Robert Aspirin, Stephen King (Dark Tower series is fantasy), Glen Cook, Terry Prachett, David Eddings, and of course the various D&D novels plus all the terrible fantasy books I read by authors few people remember. As far as fantasy books are concerned, new material wasn't lacking in the 70s, 80s, or 90s.