In fact, your suggestion makes sense, but you must remember that this is a videogame, and top level teams already have too much advantage against lower division teams. A great cup prize makes the cup more interesting to lower division teams. 1.500.000G in a D division team is a great boost, 800.000G? Not that much... and i believe they try to let lower division teams the chance to grow faster if they do things right, that's the reason i believe that cup winner might play WCC if their league rating is high enough too.