Have you realized that they're going to have to come up with a series finale or inevitably cancel the series?
Because there's no chance of them adapting the entire One Piece manga.
Because if (according to themselves) they spent a lot of money just to produce East Blue, then they won't even be able to get to Marineford, because it's too expensive, actors will already be older than necessary for the role, i.e. , this series will not go very far.
The safest way is to invent an ending or use Oda's initial idea that One Piece would last only 5 years (which was not possible due to the Warlords).