Why does the IndoorHub use a different SSID and channel from the outdoor Hubs?

The answer is simple: so it can be successfully connected to an AyrMesh Receiver. If the IndoorHub had the same SSID as the Hub and the Receiver was able to "see" it, the Receiver would immediately connect to the IndoorHub instead of the Hub (and the network instantly would fail). It uses a different channel to make sure it does not interfere with the Receiver's reception of the Hub's signal.