Previous discussion (2 days ago): https://news.ycombinator.com/item?id=37734685
(It's on my list to do more for submissions like that which accrue a bunch of upvotes slowly but never break the front page...)
(1) if we didn't do that, commenters would start asking "why are there a bunch of comments here older than the OP they're commenting on?" - and our experience is that this leads to more confusion than the other way around; plus
(2) it seems unfair to have all the comments on the earlier thread plummet to the bottom of the new thread because they're so much older.
This topic comes up regularly in a slightly different context, which is re-upping stories that make it into the second-chance pool (https://news.ycombinator.com/item?id=26998308). There are a bunch of past explanations here in case helpful: https://hn.algolia.com/?dateRange=all&page=0&prefix=true&que....