There really exists no good reason that you would want to have the same UI across all of those platforms, for anything beyond the toy examples that the Windows Store has been plagued with. The display and input device constraints are nearly disjoint, unless you go to an incredibly basic common denominator.

I've always been a Windows dev, and I've never seen a compelling reason to take up UWP.

I disagree. I think UWP has done a really good job technically behind the scenes, but poorly explained publicly of showing how one device's display and input device constraints are another device's accessibility/ease of use guidelines. That the basic "common denominator" made things easier/better to use in general for everyone, even if users/devices were capable of fewer constraints and more guideline breaking.

In addition, UWP and Fluent Design System had a hard time coming back from "these are the constraints in all situations" to "here's how you flex when these are the constraints of the current system versus when they are merely guidelines that you can break if your user accepts it". That became a focus in Fluent Design System 2.0, but it certainly does feel like it may have been too late avoid the "worst common denominator" branding that Fluent and UWP got painted with early on.

UWP/Fluent did a lot of things right technically that Apple should apply to efforts like Marzipan, they just might not realize it based on the tarnished brand.

>Windows 10 Mobile

And all their 5 users?

Are comments like that really necessary?

Necessary no. Hurtful? I don't think so, if I may say so myself.

It's a comment to put into perspective the relative insignificance of the platform -- and thus that the statement of the parent that it supported that too doesn't amount to much.

It also shows how MS effort was either badly thought out from the start, or at least failed -- and all those cross-platform touch-first changes of Windows UI where later toned down.

Sure it is. We must never forget that one of Microsoft's biggest selling points for UWP, and by extension the Microsoft Store, was to port apps to a platform that was, frankly, dead on arrival, at a time when the vast majority of Windows users were using mouses and keyboards.