Damn! This is helpful, but at the same time vexing. Are you saying that instead of a prologue, one should set everything up in the first chapter?
I guess that's the key question, isn't it. Most of the time I find that the material in the prologue either could have been chapter 1, or really could have been eliminated in terms of "set up," and the information just provided to the reader more naturally over the course of the story itself. I like the advice "start at the beginning," and to me a prologue, by definition, says you are starting somewhere other than the beginning.
Hopefully it goes without saying that this is my personal view and I also believe that each writer should follow his or her own vision of a story. If that vision includes a prologue, then so be it. But perhaps some of the criticism of prologues generally can help people avoid problems with theirs.
One thing that happens a lot in fantasy is that a writer develops a ton of backstory, history, culture, and all of the other things that come through world-building, and they take the view that the reader is damn well going to hear about it whether it is necessary or desirable for them to do so. Prologues often include that sort of material as well. In my view