Why do I have to pair my devices again after changing the Bluetooth adapter?
Every Bluetooth "thing", for lack of a better word, has a unique identifier. If it didn't, devices wouldn't be able to differentiate from one another. Walk down the street with AirPods here in a month or two and without a unique device identifier, you would get everybody else's music/conversations/whatever coming through your AirPods as you got within ~30 feet of them.

Your paired devices are still in that list because your computer remembers devices that were previously paired to it.