Why did Windows 95 setup use three operating systems?

I was looking for a blogpost from many years back about features Windows cannot provide, because it would result in logical inconsistencies if multiple applications used the feature. The blogpost gave examples like setting the desktop background or file-application associations "definitively" from applications, and mentioned at least one example of two applications fighting resulting in some chattering in the Windows UI.

I thought it was Raymond Chen's blog but I haven't been able to find it. I thought someone here might recall and have a pointer.

"What if two programs did this?" https://devblogs.microsoft.com/oldnewthing/20050607-00/?p=35...

This is a recurring theme featured in multiple of Raymond Chen's blog posts, though. This is just the earliest one I can remember.

Here's a few more: https://www.google.com/search?q=%22two+programs%22+site%253A...

The "what if two programs did this" mantra I learned from these blog posts helped me greatly in judging whether certain feature requests from users make any sense at all. As soon as it involves touching system configuration, even if there is an API for it, it's probably a very bad idea.