Ok you guys, since this has been posted 4 times, there's obviously an appetite to discuss it, so I've turned off the user flags on the original post and merged the comments thither:
The basic ranking algorithm is determined by points and time, but the software provides ways to override that. One of them is "moderation penalties"—which means downweighting the post, so the actual rank of the story is lower than the basic algorithm would predict. The degree of downranking depends on the particular weight that the moderator decides to apply.
In cases where we're merging thread B into thread A, it's not in anyone's interest to have both A and B hovering in the user's face, so once we've moved all the comments into A, we apply the maximum downweight to B.
https://news.ycombinator.com/item?id=42583297
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