Dang has actually written a response to OP a few days ago, saying essentially that he understands the intention is good, and that this sort of automation is at odds with the core philosophy of HN existing to promote curiosity and interesting conversation between human beings. When a post is popular enough, the community tends to organically post the un-paywall links, making the bot unnecessary.
Imagine having machine-automated archive link posts on every NYT and WaPo submission, it would be annoying and the early comment count would become meaningless noise, not even indicating that some person found it interesting enough to dig up the archive links for.