They should've made a new series from this point onwards like toei did with dragon ball z. As we know, OP isn't that popular in north america, just like db wasn't popular before DBZ. OP could've attracted new viewers if the ones who never gave it a shot didn't feel like they have to watch more than 600 episodes to catch-up... and that could only happen separating the anime in two parts.

Of course the japanese doesn't give a shit about the americans. They are only thinking about themselves. So I understand that they want to keep OP as it is since it has been a huge success in japan.