Windows did have and to some extent still has many crappy, old drivers that reduce system stability. We don't need to encourage that on Linux.
This is ideology. In real-life, some OEMs are binded by NDAs (so they can't do all what they'd like), and the split between hardware and software is quite blurry (chipset vendors don't want to disclose their secrets by open-sourcing their code).
I wish like you that more code would be supported in mainline kernel (just as I wish every single board would support SystemReady/UEFI or any similar solution (ideally more lightweight) so that they could boot a generic kernel just like x86 does (and regardless of the availability of the proper dts for this specific board, which may be hard to download after several years)). But this is not the world we live in.
Because of this "stable-api-nonsense" ideology, we end up with piles of junk (e.g. all old smartphones and boards that become unsupported after 2-3 years... and we only have one planet !) while we can still easily use 10-15 years-old PCs.
This can be solved by offering a binary firmware, can it not?
Imo the responisibility lies with the hardware vendors. Sell your hardware with working software, and support it for x years guaranteed. When the support period ends they can decide to extend it (they wont, but they could) instead of relying on developers who have nothing to do with the product and are working for free for the hardware vendor.
Either that or contract kernel maintainers to upstream it for x years and they do the heavy lifting, but that's always going to be more expensive than doing it in-house.
They already hire kernel hackers to build their drivers and bespoke images in the first place.