I mean for the Microsoft Android phones it kinda makes sense, since they're not exactly shipping Android by choice. They'd much rather you use the Windows Phones which this says ARE locked down.
Apologies for being unclear, it's true Microsoft didn't have the option of Windows Phone for their Surface Duo devices, so they had no choice but to use Android. To clarify, when I phrase something as being an unwilling outcome it does not mean both were equally viable options and they picked the one they wanted, rather that Microsoft's hand was forced due to this development. I hope this helps.
They mix up Google-vendor (pixels are absolutely the best and most unlocking-friendly hardware at this point), with Google Play Services services/limitations (ie dominant player in android ecosystem) AND Google, the dominant contributor to AOSP project.
And it's also partially false, as Gemini works just fine after unlocking/relocking, and all the advanced features (full performance of the cameras, NPU access, secure element) work even on non-Google OS. Things that do not work (mostly wallet) are valid issue, but then again, they work just fine after flashing OEM firmware And relocking The bootloader.
So I can only guess the quality of the contribution is similar with other phone brands.
This proves there is no technical difficulty to provide unlock bootloader