I think that has to do with a few things.

First, we can't assume that the person who used it was the same person who stored it and kept it. if you throw a razor in a drawer and bang it around, then move to a new house and dump it in a chest of grandpa's old stuff... (see where this is going...) you can't have the expectation that the razor will be in pristine condition.

Also, oxidation will dull a sharp edge. If a razor were oiled and sealed well you might avoid some of that, but if it was just wiped dry and put away and never touched again for years, you'd likely lose the edge just to oxidation alone.

Those are just my first thoughts.