Im pretty sure it is supposed to be there but it's been bugged for years? It doesn't always appear when submitting art on existing characters too.
The 4MB size cap itself is wonky as well, more than once did I submit 'big files' that were under 4MB but the site still viewed it as too big (like 3,8MB).
So yeah, it's there but utterly broken and in need of fixing I think.