It allows configuring while not near it too, to check what's wrong with it while at the office. Bluetooth doesn't extend that far.
There's absolutely no reason your private home router should be a slave to whatever remote configuration, monitoring, or intercept that some third party may be under legal orders to implement.
IMO these devices are nothing but parasites. On the positive side, Google has no track record with selling this kind of device and hopefully they will fail badly at it.
Maybe I'm over-stating the similarities, or the actual success.