They can afford it but it probably won't increase Windows revenue, which is anyway only ~10% of their income. If they could make upgrades that people would pay $$$ for like in the Win95 days they'd be motivated to try but desktop OS is a mature segment, and people expect updates to be free now, so it kills the incentives to do anything.
I spent a good few hours contemplating this over the last couple of years and the only rational answer I can find is that they are, apologies for language, just complete fucking morons.
I drank the WinRT Kool Aid between Windows 8, Windows Phone and the clear failure of Project Reunion.
Still I keep myself around, expecially to warn newbies that whatever Microsoft is selling for WinUI, regardless of the shiny cover, the book inside is roten.
Whatever I have learnt from community calls and endless Github discussions, is that most new interns never did Windows development before landing on Windows team.
The calls are available on YouTube, mostly young, puzzled looks when questioned about feature XYZ coming to Windows, not even understanding issues that come from Windows 8 and 8.1 UAP model, that predated UWP, among other possible examples.
I would dare to say they did all their studies in UNIX world, Apple, Google devices, before landing a job at Microsoft.
So Web technologies it is.
Note I am not blaming them, each one gets to learn what they can, how they can.
The blame lies on upper management of a 4 trillion valued company, that isn't able to put in place the resources and learnings, so that the team can actually deliver, as it used to be during the 3x "Developers!" dance.