I’m seeing exactly the same thing. Certain companies re-listing the same position for months on end, despite hundreds of people applying.
According to this article I read recently, some companies are either doing it to give the illusion that they’re thriving and planning to take on more staff, or just to keep a pool of potential applicants on the back burner just in case.
It sucks. I’ve been looking to make a career change for over a year, and have only had two interviews despite sending out literally hundreds of applications.