I do find this kind of theorizing to be one of my favourite, which is working out the what and why.So anyway allow me to take a video game far to seriously and give my ideas.
As you rightly said, Stalfos come from being lost in the lost woods, however they are not stuck there and can't be found in various different locations and dungeons throughout the Zelda series. So they at least are no locally bound, even though there point of origin is. The wide dispersal of ReDead does not then stop their origin being based on a certain region.
Personally I do not think that area is the result of ReDeads. Magic is often considered to be the cause of ReDeads as has been stated by others in this thread, however the idea of them being cursed has always appealed more to me. I make the distiction between magic and curse because I would say that magic tends to assume an intentional act by an evil being or a reaction to exposure to intense evil magic. However a curse could come anyone or from an action. For instance they may have committed terrible crimes and were cursed either by the people or by the Goddesses into being Zombie like creatures. I don't know why but the thought of them having been evil and being cursed that way rather than being lifeless corpses animated by magic appeals to me more. There are a many different types of dead creatures still roaming (Poe's, Stalchild's, Gibdo, Stalfos) and I do like to think of reasons for them. The only one I find difficult are Gibdo in the sense that it is hard to separate ideas from the and ReeDead.
