Apparently Square and Namco seem to have a good relationship going, plus I don't remember 2B appearing as a guest character anywhere since Nier: Automata's release, so they acted as quickly as they could. To be fair, I don't think Setsuka and Hwang will come back as playable characters, Cassandra might though, maybe Yun-Seong too. Also, remember, season pass 1 for Tekken 7 didn't even have one legacy character.