Probably because he doesn't know that while the link doesn't show up immediately on the main thread for new comments, he can visit the comment he wants to reply to itself, and it will have one.

I am wondering the same actually. I wonder if he could paste his comments as replies and then a moderator could make dead the ones left as main comments. As it is the threads are quite hard to follow.

Sorry. I don't talk to talk a lot on HN, :P