Why are YC company posts' comments disabled?

It's an ads, the only type of ad on hackernews

https://news.ycombinator.com/newsfaq.html

"Another kind of job ad is reserved for YC-funded startups. These appear on the front page, but are not stories: they have no vote arrows, points, or comments. They begin part-way down and fall steadily. Only one is on the front page at a time."