Google did user agent detection and would actively redirect Windows Phone users to degraded experience versions of things like YouTube and Maps even if the full versions would work fine.

> ... even if the full versions would work fine

That's quite a statement, given that Internet Explorer didn't support WebGL, nor rich HTML5 video reproduction, until 2014 [0]. They are needed for the full versions of Google Maps and YouTube, respectively.

Microsoft did create a YouTube app, but it filtered out video ads, which didn't sit quite well with Google [1]

It looks to me that the pain was self inflicted.

[0] https://www.cnet.com/tech/tech-industry/windows-phone-8-1-fe...

[1] http://allaboutwindowsphone.com/features/item/24422_Thestate...

I'm speaking from my own experiences. Proxying the requests to rewrite the user agent, the full mobile version of YouTube and Maps worked properly. Without rewriting the user agent I would be redirected to the minimal versions of the websites which had poor experiences.

> There were PWAs of the most popular Google products that worked just fine in Windows Phone.

No, there weren't. PWAs did not even exist at the time. User experience was severely degraded when browsing Google properties with Windows Phone IE.

Google also barred Microsoft from releasing a native YouTube app for Windows Phone, insisting that it must be done with HTML5 instead, even though Google's own YouTube apps for Android and iOS were native.

> Microsoft didn’t do the same with theirs. Outlook didn’t get an Android version until late 2015, Edge took a few years to arrive, and Bing Maps never made it.

Bing Maps works fine on Android as a PWA. It does not get degraded if I use Chrome. So yeah, Microsoft didn't do the same with theirs.