Because it is still running S1 as an OS? Factory reset (no idea why this was done) does not change the OS, it merely erases all information stored on the device, and sets the software back to what it was when it came out of the box. 

You’ll need to connect it, I suspect, to an S1 system, and update it to S2. Or call Sonos Support directly to discuss it.

When you speak directly to the phone folks, they have tools at their disposal that will allow them to give you advice specific to your network and Sonos system.

Hi,

When u say ”update it to S2”, what us ”it” and how is it done?

https://support.sonos.com/en-us/article/update-to-the-latest-sonos-app-using-the-s1-controller

And ‘it’ is the Sub gen 1 you’re having difficulty with. And if you no longer have an S1 speaker to connect it to for upgrading, that call to support may be required, I’ve never had any S1 device in that state.