Doing that would open them to the possibility of a competing stack that could push out the default Windows one, similar to a different Linux distro. Also, they wouldn't be able to be kings of the system and force whatever they want onto you, because you could then switch away to a different NT-based distro. They just wanted the hackers to go away, it's simpler for them.

The closest they ever got to a 'nothing' NT was something like Windows Core or Factory/Validation OS. They still ship with some windowing capabilities, but they could strip them out if they wanted to, because there is a barebones text-only mode in Windows. Of course, all these editions are or were tightly regulated and only issued to big businesses who are supposed to have them, it's nothing that a Linux user would want.