I think it's likely that Microsoft is running a process to correlate "new" GDIDs to old ones, ex:
"Oh look, this one has almost all the serial numbers of components and attached-devices as that other one, it's probably the same computer with a fresh install, let's make a note of that..."
They do not need this, they require you to create a Microsoft account to use your own computer (currently without a phone number, passport and selfie but that will probably change in the future).
But I've got nothing to hide