Because it is still tied to the original purpose of the site. Being an offshoot of ycombinator means the focus never shifts and it doesn't have to follow trends

Because it is still tied to the original purpose of the site. Being an offshoot of ycombinator means the focus never shifts and it doesn't have to follow trends, it just is a place to talk about tech and tech startups. It doesn't have to update the ui to stay popular with young people, it doesn't need to have a crisis moment or pivot to a new idea. It can't be replaced by a tech alternative as it's not in competition with other forums for eyeballs and income. It's not really run like a business, I guess.