Best answer by Stuart_W
When you originally set-up your first Sonos speaker you were required to provide your account details or create an account. This has been confirmed by Sonos and the long term users (It certainly is true for me). It's your prerogative to dispute this but it's rather rude.
Now there are a couple of things that could be happening here. 1) You may have purchased a Sonos unit which hadn't been factory reset and already had somebody else's account details. 2) Sonos over the last few months have made it a requirement to login when accessing certain system functions such as adding components. That means it is entirely possible a system went 8 or 9 years without needing a login but now is likely much more regularly.
If you don't like giving Sonos your information then create a Sonos only e-mail and allocate the bare minimum information.