Baku must have known that #0 was going to arrive, because he even hinted at Yakou eventually challenging for it just a few chapters ago, so maybe the goal here is to get some intel about #0, and I also believe that Baku knew #0 would arrive, because one of the goals is also to protect the radio tower, and what better way to protect the tower than not only with a bunch of Kakerou members, but also some of the baddest dudes in Kakerou around. I also think that Baku is still picking at L-File members as well, and maybe the leader even anticipated on that.