I can smell Imu making an alliance with BB from a mile away.
Imu realizes he needs pirates to deal with pirates and maybe he already used Davy Jones like that.
Like in the Pirates of the Caribbean movies, Davy Jones is used by the government. Imu pulls up to Hachinosu, offers to BB to join the WG if he deals with Luffy.
Akainu is pissed off because BB joining -> Marines are divided -> the world is divided.