> The ... UI of Windows 8 and the Windows Phone... underrated in my opinion. It was ... focused on touch.

That's why it was rated low. Most people were using this interface on PC's and laptops, without a touchscreen, where a touch-focused interface does not make sense. Maybe it was good choice for Windows Phone or Windows Tablet, but people were not rating it based on that experience. The very idea of using a single UI for both a touchscreen-oriented and no-touchscreen, kbd-and-mouse computers is the most problematic aspect of it.

> It was simple

No, it wasn't simple. There was the simple part, but things not integrated into the simple part were a hodge-podge of previous Windows versions' UI. Now, I like some of the previous Windows versions' UI, but putting a simple veneer on something does not make it simple; if anything, a little more complex.

> It was fast

The fact that an OS UI in the 2010s or 2020s need to be commended for being fast is kind of sad. Plus - I don't believe it was that fast. Did you try running it on, say, a 15yro machine relative to the Win8 launch time? i.e. 1998? Even with a 10yro machine I believe it was kind of sluggish.