This wasn't posted in /r/programming, though; it's /r/reddit.com, a general purpose subreddit that new users are subscribed to by default, and that has double the subscribers compared to proggit. I imagine lots of new users unsubscribe from proggit but not from /r/reddit.com; anecdotally speaking, reddit's becoming very popular among my non-programmer but internet-familiar friends who like pictures of cats and rage comics.
That isn't to say to that proggit isn't pretty different to HN; going on there now (having not visited it in a while) only a handful of links show as having been visited due to my seeing them on HN. The content there is different and the level of discourse is acceptable, so I like it.