Best answer by Stuart_W
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.