Now that the previous has expired, back to the explanations.

What is the appeal of stand-in characters? They may or may not be some form of Sue, but more specifically I am speaking to the character designed specifically to get the audience to sympathize with them and more so, step into their shoes and live their story vicariously. Now, I have heard many reasons for this, but almost universally are these same figures panned for not having much life to them and being cardboard cutouts and not actual people. In some cases, they even inadvertently prove to us viewers, especially outsiders, why said characters are not even functional human beings, or related to them in that regard. 

We all know the worst of the worst examples, but why in general? Grasping the attention of a reader is of course crucial, as otherwise they will just seem themselves elsewhere, but why make some of these identities so hollow and reusable that anyone can be them? They sometimes span entire genres of creative works, where there are a number of trope-ish types of characters who people can fill the shoes of as the reader or viewer, but is it really that strange to not do so and instead view them as independent agencies and entities? That it is more important they are their own characters first? Making them distorted fragments of real people, twisted reflections, seems to work better from my experience.