It's a much bigger drop than expected. The explanations I have seen so far point to HF21 reducing author rewards from 75% to 50%, and all posts/comments that would get under 20 STEEM get further reduced, while those that would get over 20 STEEM receive an extra bonus.
My upvotes went from just under 5 cents, to just over 2 cents. I can barely make posts pay out without help... I had read all the announcements but was still unprepared for the drastic drop in author payouts.