As for the why, have you ever tried installing vanilla Windows on a modern notebook? I know Linux has a reputation for bad driver support, but in my experience with Dell, Lenovo, and HP, a vanilla Windows installation will have no graphics driver, no network driver (neither wired nor wireless), sometimes the sound drivers are missing. It is a shitshow. Meanwhile, Linux on the same machine generally works out of the box.

But the answer to the question "Why do OEM versions of Windows even exist in the first place" is that without OEM customization, a Windows computer is a non-functional computer.

I think the driver situation has vastly improved from Windows 7 and even more since 8 and 10.

I have reinstalled Windows on quite a few laptops and desktops and have been quite surprised with how much works straight out of the box these days (mostly everything in my experience, bar some stuff like Fn keys). YMMV of course.

So how do most corporate IT teams build SOEs?

He was talking about out of the box functionality of linux vs windows.

Of course you can build SOEs with manually assembled sideloaded drivers, especially if your organization uses just a handful of different models.

At the enterprise level it is quite common, specially since they want to have control over every little piece of software that goes into the stack, including updates.

I even worked at a few places that created their own UNIX flavors (mostly GNU/Linux based).

They get the drivers from the OEMs.

They are also paid teams to put the image together.