This is a great point, but it's also about there being clear winners.

Wherever we had a clear winner (like Freetype for fonts, where even TeX engines converged to them, or XKB for keyboard layouts, where console layouts were converged to XKB approach, even Ubuntu was to a large extent because everyone targeted it...), something became a defacto "standard".

Now, combine lack of coordination with people recognizing there are winners, and you get the ecosysten we have today: everyone thinking they can do even better and hoping their solution is the winner to end it all.

IOW, why is NixOS the solution, and why couldn't the group behind it help evolve RPM or DEB to have comparable features?

I think it's more accurate to say that systems without governance (decentralized?) can't coordinate, because in order to coordinate, there must be ways to onboard newcomers, communicate changes, and resolve disagreements. Additionally, systems without hierarchical governance can barely coordinate (e.g. early Wikipedia, r/place), and the most coordinated systems have a strict hierarchy with either a single leader or closely-aligned leaders.

In order for a protocol like LSP to take off, people must unite behind it. A common issue is that when someone creates a protocol, but others adapt it incorrectly, because they disagree with and/or don't understand some parts. Another issue is that the protocol has a design flaw, so the original creator tries to change it, but the change only goes to some implementers (who may disagree with it or apply it broken). A big company like Microsoft sidesteps these issues because the adopters are employees; being paid, they're motivated to work without disagreeing, fix their bugs, and finish the project, and it's easier for them to communicate with the creator (or at least someone more familiar with the protocol) for guidance and changes.

I'm not super aware of Linux's history and organization, but I believe it has a strict hierarchy with a dictator (Linus). Anyone can submit a patch, but if the patch ignores conventions or otherwise conflicts with other code it will (rightfully) be rejected; you may change those conventions or code if you gain influence and/or convince others, but then they're changed for everyone.*

There are other OSS projects that are widely successful, all (that I'm aware of) with strict governance: e.g. LibreOffice, KDE, Blender, and Rust. In fact, I'd argue KDE is "Linux on the desktop" and works well; there are issues but only because KDE has limited funding, must work on hardware from uncooperative vendors, and people are used to macOS and Windows (if Apple or Microsoft had limited funding, no in-house or connections to hardware vendors, and macOS and Windows weren't already popular, they would probably fare worse than KDE). The author's specific issue highlights a problem with decentralization: he's using NixOS which is separate from KDE. His issue would be solved if the NixOS team became part of the KDE team, or the NixOS team created its own desktop, so that either way the OS + desktop would be under one organization.

I think there are lots of advantages too, to the lack of coordination. For example, Linux OS updates were much leaner for me than MacOS system updates, which are always trying to push endless new features that I don't want (like Apple Intelligence). Linux has to do the bare necessity to survive, rather than a coordinated attack against the consumer to constantly upgrade.