Ask HN: Why doesn't HN have a comment notification system?

HackerNews is a platform with very rich content.The Front page contains very interesting topics . Also most of the times discussions are food for thought . I enjoy reading them. Comments are very mature than the ones on sites like Reddit. My point : Why notifications have not been implemented for comments? And Direct messaging feature will also help the like-minded people to meet on this platform. Is there any philosophy behind not implementing these features?