Charts showing Hugo/WSFS award finalists and their rating counts on Goodreads

Hugo Award - Best Novel / Best Novel or Novelette

If you're going rail against the 'niche' works nominated by 'the voting body of "fandom"', then perhaps it might be a good idea not to have the least read Hugo finalist of the decade on your slate?
Dune World in 1964 uses the stats for Dune. Wheel of Time (series) in 2014 uses the stats for the first in the series. (Perhaps the final volume might be a better pick - as of late May 2017, it's at 94k ratings.)
Noticeable upward trend at the bottom of the range, with the big outlier being 1991, with a book that seems to have gone out of print almost immediately.
What happened between 1964 and 1965 such that every finalist in the former has more ratings than every finalist in the latter? A (presumably) UK-centric voter base might account for some of the jump, but surely not all? Revisiting the Hugos has a few suggestions for what could have been more popular finalists.

Lodestar Award for Best Young Adult Book

This chart is a bit of a mess because (as far as I can tell) ISFDB doesn't record the year the Retro Hugos apply to, just the year they were awarded, which could be 50, 75 or 100 years difference. It wouldn't be impossible to either (a) have some hard-coded hacks with the "real" years and/or (b) use the first publication date of the nominated books to work out the "real" year, but right now this isn't something I'm interested in doing.
The Sword in the Stone in 2014/1939 is probably under-reported, as it appears in the omnibus The Once and Future King, which has just under 90k ratings as of May 2019. This is the publication which provides the ratings count for The Ill-Made Knight in 2016/1941, as seemingly no stand-alone edition of that volume with an ISBN has ever been published, and so these charts have to fall back onto the omnibus edition in the absence of any other option.