If you are talking about the "jobs" link at the top of every page, then
those are essentially advertisements from YC-funded companies looking to
hire people. You can't up-vote, flag, or comment on them. Think of them
as a clickable banner advertisement that starts at position #6 on the
front page, and quickly sinks. When you realize that the success of YC
funded companies is what pays for the existence of HN, then the job ads
makes sense.
The HN site guidelines linked at the bottom of every page say to not use
HN for contacting or communicating with YC, or YC funded companies. This
pretty much explains why comments are disabled on the advertisements.
HN also has automated, monthly "Who Is Hiring?" and "Freelancing/Seeking
Freelancer?" posts available to everyone.
https://news.ycombinator.com/user?id=whoishiring
https://news.ycombinator.com/submitted?id=whoishiring