"BT routers come with randomised passwords and I see no reason to change them to something user-selected and likely less random. That must make up a large fraction of the 82%."
But my (non-BT) router has the random looking Wifi passwords printed on a label on it. As does the router supplied to a mate by his ISP, Liberty Global (the owners of Virgin Media).
And everyone's got cameras on their phones now, bad guys too,