That area around the heel counter and opening is where the cross-section of the leather membrane is exposed and it is a high stress area with some kind of rubbing every time you put on and remove your footwear. Take a piece of cloth that's unfinished or poorly finished at the edges, that unfinished edge becomes a weak link and will unravel. With leather, an extended and improperly trimmed finish may cause peeling to occur.
This is why certain shoes are made so that the leather fold inwards into the lining and does not expose the cross section of the leather to high stress areas. Hopefully, I am making sense with what I wrote.
I've had a 8 year Alden peel exactly around the area and have seen many specimens of vintage shell that suffer the same area. I've made it a point to condition the area around the opening on all my shoes now.