I don't know how HN is built, but given its history in Arc, my guess is that the data structure that holds comment threads isn't optimized for a ton of branchin

I don't know how HN is built, but given its history in Arc, my guess is that the data structure that holds comment threads isn't optimized for a ton of branching. Threads with that many comments don't happen very often, so it's probably a low priority fix.