The "Linux Desktop" is not and has never been a thing beyond a vague marketing term. What you're thinking of is a loose collection of unrelated projects. Pick a single stack and go with it and things get better.

....Which might be one of the reasons Linux Desktop is so awful to develop for.

You wonder why people ignore your platform? Saying it isn't actually a single platform and instead is dozens of different platforms just means each of those platforms is even less relevant. Saying you're not just one platform with 10% market share but actually 20 with 0.5% each doesn't make the case for shipping on Linux Desktop any better.

I'm not making a case for shipping on the "Linux desktop" because that doesn't exist and has never been a real platform. Most smaller distros are not trying to be "relevant" to whatever the gaming community's fad of the day is. They're perfectly fine filling what niche they do. If you want to target those smaller distros as a platform, you can give them some source code to work with, or you can pay all the cost of maintaining things yourself, or you can just ignore those. They will do fine without your game.

So what are you saying? Developers should just choose a major distro and target that, then get all the flack for issues their product has on every distro that isn't supported? Because that's basically what's already happening and developers hate it, which is why they often don't ship on Linux at all.

And many proprietary pieces of software license components from other proprietary pieces of software, so that even if they did want to open their code they'd have to strip pieces out of it anyway which doesn't really help the cause of distros integrating it. And even if it did, then the developers are reliant on the maintainers for their relationship to their customers. Have an issue with the product? Oh, it turns out that's because of this patch made by the maintainer of the package for that distro, who now has to be contacted and convinced to fix it, which they may decide not to for arbitrary reasons. Even open source developers have problems with this!

In general, distro maintaners can't help you with legal conundrums you created for yourself (you signed restrictive NDAs and proprietary license agreements and didn't consider the fine print until it was too late) or with other unrelated market problems (lack of popularity, lack of developer interest in supporting your game).

If you need to strip out some parts and there is enough will in the community to replace those pieces that you stripped out, then it will happen. If you have a product that is anywhere near being popular among the FOSS developer communities then I don't think it makes sense for you to claim that this will doesn't exist, or that distro maintainers will lose interest.