This is because the name "One Piece" was registered maliciously, and the company that registered the name has not published any products under this name. The translation of "One Piece" first came from Taiwan. Later, the company that introduced it went bankrupt, so the copyright was transferred to Dongli. However, that company had the right to use the name "One Piece" and the name "Luffy". It was registered and sold to Dongli for several million, but Dongli refused. This is why the One Piece books published by Dongli are all called "One Piece" and why Luffy is called Luffy. Later, the mainland also continued to borrow the name "One Piece".