Because Zoro isn't the MC, he doesn't get nearly the same screen time that Luffy gets, so it's more accepted that he doesn't have huge character development.
BUT.
Zoro does have character development and it develops very slowly, with him starting not giving a shit for Luffy's dream and only his own, to giving up his life for Luffy's dream in Thriller Bark.
In the Post-TS Zoro has given almost 0 screen time for Zoro, only trash fights against meh characters. Wano is the first time we got more from him.
All Straw Hats got shafted in the Post-TS for Jesus Luffy, and the Luffy schtick got old in the Post-TS.
Every arc is Luffy gets there, gets invested in the people, fights the villain, defeats the villain and save the people, move on.
In the Pre-TS this worked better because every arc was about another Straw Hat besides Luffy and we got more intereactions from him with the crew, in the Post-TS is the Luffy show and he only interacts with a few characters from the land he is saving and the villain, every single time.