Units will continue to be listed here until they are assigned to another owner.

One of the excellent reasons to factory reset a device before getting rid of it. When the new owner registers the device, it gets removed from your ‘account’ and shows up on theirs.
 

But I have old devices that show up on my account, they really don’t matter. No one except Sonos cares that at some point, I owned some BRIDGEs that I have long since recycled. 

My challenge is that the device died years ago. There was no possibility to factory reset it or register it with a new user. So I guess I’m just stuck with it there? (Assuming there’s no way to request that it be removed?)

Even factory reset devices stay in your online account until they are registered again against a different account.

Depending on the device it may get marked as eligible for an upgrade discount. I still have long dead ZP80 and ZP100 visible which both had hardware failures, another ZP100 which worked last time it was plugged in and my original cr100 controller which was not much use without the ZP devices so is also long gone.

Randomly one of the ZP100s became eligible for an upgrade discount during the past 1-2 years, maybe it was the surviving one I plugged in to see if it still worked 

Never really been bothered about what products are listed in my account I so rarely look. So even though it was a surprise to find the original devices I have never given it a second thought.