25 points means OP isn't the only one interested. I, like you, am not sure what caught so much attention though.
What causes this phenomenon on HN? I find this happens a lot, where some longstanding project or old article or something gets posted and makes it to the front page without any context as to why it was posted. I'm left to hunt down what made this relevant or what is new on the page that made someone post this and made others upvote it, and often I can't figure it out at all. It's a bit weird.
Obviously it could happen for any number of reasons but my guess is that the most common reason is that someone encounters something for the first time and thinks "this is really cool" and wants to share it with someone, and then they think "I know, HN will love this!" and then they post it, and then they either get distracted and wander off, or they see everyone posting "why are you posting this, it's been around forever" type of stuff and they decide they have better stuff to do.
The way I think of it is by going back to how PG once described HN as YC's university campus. Like a college campus, people come through, some stay, some leave. Each new class has to learn some of the same lessons... hence some history, and some classes/topics, repeats with predictable periodicity.
Doesn't mean it doesn't bug the old hands to see the same thing come through again and again. :) And links to old discussions occasionally dig up useful old learning.