Bluetooth connections frequency hop among 79 bands to avoid interference. That way, you don't have to pick one channel and hope it stays clear, you just switch frequencies constantly and deal with the occasional hiccup. That means that when you pair devices, they share a key that synchronizes the pseudo-random choices for what frequencies the connection will use over time. So each connected device needs its own broadcast, because other devices won't be listening on the same frequency at the same time.