A factory reset will not remove it from the list of purchased devices at www.sonos.com. The only thing that will remove it is it being registered to a new owner, which then will ‘transfer’ it off your account.
I have at least one Sonos BRIDGE still there, which I recycled years ago. At this point, I just ignore it. Yes, I purchased and used it, no, I didn’t give / sell it to anyone else to use.
It isn’t a list of what is ‘active’ on my system right now, it is a list of ‘this is what was registered to your account, over all time’.
