Fighting games need to be sustainable over time so they sadly do this to keep interest over time with anticipation. That said, just because a character is in a functional state doesn’t mean extensive balancing work and such. Trailers always make things look like they’re in better shape than they truly are.
Either or, most devs continue developing even after they’re done what’s planned for the base game in preparation for whats to come next. After waiting like 6 months to even hear about what was in Ni no Kuni II’s dlc. They started way later clearly. But that’s an issue in itself.
But in the end it’s always about maximizing profits


