Why? Most users don't want them. And for those that do, there's https://www.hnreplies.com/, as well as other options mentioned elsewhere here.
“So the most important thing a community site can do is attract the kind of people it wants. A site trying to be as big as possible wants to attract everyone. But a site aiming at a particular subset of users has to attract just those—and just as importantly, repel everyone else. I've made a conscious effort to do this on HN. The graphic design is as plain as possible, and the site rules discourage dramatic link titles. The goal is that the only thing to interest someone arriving at HN for the first time should be the ideas expressed there”
http://www.paulgraham.com/hackernews.htmlI mean, you only have to read literally any thread on HN's design and features, or any of the nigh-weekly threads complaining about the modern web and its complexity, how commodification and capitalism have ruined its creativity and quirkiness, or how javascript exists, to see those sensibilities are alive and well and strongly culturally correlated to the layout of this site and the perception (somewhat inaccurate) that it exists frozen in amber.