It is absolutely and undeniably a real phenomenon. Take your pick of explanations, nobody actually knows for sure, but you have to tell yourself something or you’d toss your phone out the window when you get the 40th notification that you might be interested in the exact same job that auto-rejected you the previous 39 times. Speaking from personal experience over the last year.
It's very weird. You would think the people posting the jobs might know for sure, although different posters may have different motivations. It seems something that should be amenable to some journalistic investigation, but while it's getting a lot of talk between job seekers, including in these comments, nobody seems to have tried to do such investigation to get some clues as to what's going on.