it was all downhill for me starting in 2020. I think that might have been when I started posting a lot less than I used to
Your earned Merit amount went up again more recently:
(my graph has no axis, but it starts at the beginning of the Merit system, and it's only meant to give a quick impression)
but whatever the reason everyone started blowing me away in the beginning of that year.
Merit got more abundant, while the number of posts decreased. So more Merit per post, so if you post less, you lose the race.