There's a dozen different angles all coming out at once. I'll try to summarize some.

- really wants to hire H1B, but needs to pretend to interview first for compliance. These usually have absurd requirements to make it viable to reject anyone.

- really wants to do an internal or referral hire or promotion, but needs to interview for HR compliance. These usually have such specific requirements that only the person they want qualifies.

- posts jobs because a company wants to look like its growing, even when it's not.

- posts jobs to either signal to an employee that they are replaceable, or to try and relieve a stressed employee that more help is coming. Either way, it's a bluff

- yes, sometimes you want to hold out for the perfect unicorn and are not in any way in a rush to find them. There's no distinction for this, but job posts are cheap so why not?

- outdated posts that still stay up because There's no rush to take it down.

- a technique used to lower compensation. They post a job, see how many applications it gets. If it's more than enough, they take it down (with no interviews) then put it up once more at a lower rate. Repeat until not enough people apply. This may or may not lead to interviews because the actual goal is market probing.

-purely to advertise the company instead of actually hire. Usually done at career fairs where you talk and realize there's no actual open positions.