This was years ago, sometime before the 2016 US presidential elections, and it wasn't to fuck with r/nosleep, that was just collateral damage. It affected every sub. r/the_donald was dominating the frontpage (r/all), because it was genuinely the most active sub on all of peddit. This made the tranny jannies and admins extremely mad. To stop that, they first disabled upvotes on stickied posts from counting towards their total "score" (r/t_d mods did habitually abuse that), but it didn't help, so they changed the entire algorithm.
Basically, on any given reddit post, the number of upvotes is not actually real. There's some kind of algorithm that "counts" fewer and fewer upvotes the older the post is, so upvoting an older post doesn't have the same impact as upvoting a new one. I don't think the details of exactly how it works are public, and there are probably some other variables in play.
Anyway, the point is, before the change, if a post got +10k upvotes, it was big. +15k was crazy. But after the change, it was common for newer posts to get +50k and more, and to stick to Nosleep, it became common for stupid drivel like "Don't Open The Door If A Rape Demon Rings The Bell At 3 AM Because He Will Rape You (Part 34)" to get +10k. So any highly upvoted posts from before the change got buried, because the algorithm change was not applied retroactively, older posts kept their old scores.