This has been proposed before, it's completely possible, it would be easy to do. But we don't do it for a few reasons:
1) Each entity needs its own picture. Even if the pictures are exactly the same, they are their own entities. This ensures everything shows up (in a non confusing manner) when searched for and linked to, especially via templates.
2) We could easily make a bunch of file redirects to a single master file that would show up for all usage (even templates), and we do this for a few news images because those files are very large and having duplicates of those isn't really functionally needed, but in the event accessories ever get their own icons, this would be quite the mess to undo. This is not far fetched, as costumes used to also use a system of simple icons appropriately recolored, then received their own.
3) Even though it would be easy, it would be tedious - a lot of annoying work to implement (I'd estimate an entire day of solid work, or 2-3 of off and on work), when we might have to undo it all for reason #2.
If we knew for sure that accessories would never get their own icons, then I would support this change, because it bothers me too.