Those are talent captures. A lot of times managers have enough budget to barely hire someone but don’t really have the need to justify a guaranteed expenditure. They put out a job opening to see who applies. If a rockstar applies, they’ll hire them just to get them into the company. Good people will always find a spot. If a bunch of normal people, who might be just fine workers but aren’t standouts, apply then the fake job doesn’t get filled.
I’ve canceled very real job openings because the quality of people who applied didn’t really excite me and I didn’t really NEED someone. My team was chugging along and I had a little extra budget to help out, but my team continued just fine without hiring someone else. My budget got cut the next year by about what I would have spent on the new person, which would have made me get rid of a normal person while a rockstar would have been able to move somewhere else in the company.