Why does it matter? An artist or a novice takes images for personal expression, and a photographer takes images for client's pleasure. If viewer does not like it, then viewer be damned (unless viewer is the one paying). So I think the simple answer is that people "oversharpen" because people like it (be they producers or buyers).
In my opinion there is really no right or wrong here. People use a lot of other artifacts like over exposure, under exposure, lens flare, out of focus areas in their images. In fact, out of focus artifact has become so fashionable that we have a name for it; bokeh!
The appropriate question may be what is appropriate sharpening for me on this image.
Very well said. I could not agree more.
It is a subjective choice.
That said it does take a bit of self control to not get carried away.
Also many upload services such as flickr add sharpening