I wonder how many of them are caused by internal political struggles. When you have a lot middle management they spend a fair amount of time on resource allocation, both current and future employees. So it’s a constant fight to obtain and maintain headcount.
Hiring pipelines can be longer than the planning cycle. So you may have 3 open headcount one week, and then lose it the next because some other Big Initiative should get it instead. Or the head count flip flops between local and overseas hires. Or the level they are hiring for changes. Each time this changes, new positions are posted.
Basically companies don’t know what roles they hiring for long enough to get candidates through the process.