If job ads were threads, each thread would be a generic referendum on the company. Worse, it would be the same referendum over and over.
Job ads are boring, so there wouldn't be anything to discuss other than how one feels about the company, and that's boring except to people who have strong feelings on the topic, and strong feelings on the internet tend to be negative, so the threads would fill up with negative generic comments.
I believe that the hivemind resents boring things, such as submissions where the only new information is "X is hiring", so it gets cranky and fills the vacuum with indignation, basically as the only way to amuse itself in the absence of anything interesting to discuss. It doesn't want to, it just doesn't know any better way to have fun in a vacuum. In practice, what this would look like in a job thread is "I applied in 2015 and never heard back", plus—if there has ever been a negative story X about the company—every variation of X, X, X, repeated increasingly snarkily.
Actually, it's worse. Building a business is a long hard slog. One needs to hire more often than one has scintillating new information for the community to have fun discussing. Therefore, each successive job ad would be even more boring than the previous one, leading to monotonically increasing resentment. Repetition is the enemy of curiosity.
Launch posts don't suffer from this dynamic because by definition, the startup is new, so there's something new to discuss.