Zoro is Oda's second most favorite character, read the manga and you can understand that even for a subordinate the shine that he gets is sometimes even more than the MC. How many times has Oda clowned Zoro for cheap humor? It is just that WCI was a Sanji centric arc (again Sanji was used because such an arc for Zoro would really hurt the manga), it is the reason Sanji has been used as a hype tool post TS. Luffy, Zoro and Nami are probably Oda's favorites, I think Oda also likes Law seeing how much screen time he was given post TS.