Due to issues with the method used to track shared instances, macOS currently does NOT try to open an existing instance of BN if one is already running but when launched from the CLI will always launch a new instance. This is inconsistent with Windows and Linux where we default to re-using existing processes.
https://github.com/Vector35/binaryninja/commit/0c82c95b95dd22b8faf46ee4831b8789b349d815 is the internal commit for anyone following up on this later.