Because we want to see more comments like this (i.e. clearing up confusion), and because in a thread this large it only takes a small percentage of people deciding that a comment is high-quality for it to get upvoted.
Because we want to see more comments like this (i.e. clearing up confusion), and because in a thread this large it only takes a small percentage of people deciding that a comment is high-quality for it to get upvoted.