Sometimes HN runs hiring ads from Y Combinator-funded startups. They are on the front page for a set amount of time and cannot be voted or commented on. See also https://news.ycombinator.com/jobs

Why can't users comment on ads? I can see obvious reasons why corporate partners buying the ads would want to disable comments, but is it actually good for the site?

HN is one of the few places where there is honest discourse calling out much of the bullshit in startup culture, seems odd to limit the most compelling aspect of this community.

Bear in mind, HN is a service of YC that, to my knowledge, generates effectively zero revenue. The rare YC text line ad is a more than fair compromise for this, and one would argue "HN is able to exist" is "good for the site".

If you want to talk trash about a YC startup, go ahead and make your own submission, the HN mods are pretty fair with how they moderate user submissions.

Right, and YC companies always have the option of making a normal post if they want to.

So because there is no advertising revenue it makes sense to disable comments for advertising? huh?

They should be flagged as ads

Comments on those kind of posts would quickly devolve into product hunt style sycophantry/astroturfing, or hn style caustic nihilism. Better off skipping them.