All about design & organization of the "OS". But this completely ignores the actual problem: There's no MONEY in Linux application development. So nobody makes any that are even minimally competent.
I would correct his post, though, Ubuntu had a design language and SDK, and was working on a universal desktop & phone UI… and then that collapsed because there was no money in it. Now they're just another GNOME desktop.
Elementary has their own language (Vala), and reasonable documentation and policies, and lets you ship through their "app store"… as long as you give away your source code, it's Pay What You Want, it's not enforced in any way. Anyone can just go to github and build your software for themselves, and then distribute it for free. Elementary also takes a 30% cut as if they were Apple!
Looking at the Elementary App Center, they have 160(!) mostly tiny utilities listed. A couple Sudoku games. A $25(!!!) single-site client for write.as. But there is Minder, a mind-mapper; Tootle, a Mastodon client; Notes-Up, an organized notes app. Unimpressive but not as awful as the usual Linux software. But in 3 years that's all they've made?
There's enough servers to keep Linus working on the kernel, and a lot of nerds employed in janitorial jobs, but they have no motivation to make end-user software that anyone wants to use.
Google may be the enemy of Humanity, incubator of SkyNet, a Terminator's metal foot stomping on a human face forever, but they sorta half-assed their way into making Linux usable with Android. 'droid has a ton of end-user software (if mostly terrible) because Google Pay works and isn't trivial to circumvent, or they can just shove ads in every screen. It's mostly sloppy seconds from iOS or the web, and the dev tools are awful, but it's software. So why can't those people make desktop software for Linux? Follow the money.