I worked on the team in charge of improving iOS (13) perf at Apple and IIRC there was no dedicated macOS “task force” like the one on iOS.
Luckily some iOS changes permeated into macOS thanks to some shared codebases.
It's not surprising. Macs are less than 10% of Apple's revenue.
https://www.macrumors.com/2020/04/30/apple-2q-2020-earnings/
They are risking their entire empire because (apparently) someone at Apple has an axe to grind with macOS's Unix underpinnings. And until they start getting real consequences (developer's leaving in huge numbers), it doesn't seem like it's going to stop. The tragedy is, if they ever do reach that point, where developers are leaving in huge numbers, it'll be too late. Platforms are a momentum game, you're either going up, or you're going down. And once you're going down, you're as good as dead.
To me, the idea that an OS is mostly finished is completely bananas. There's so much room for improvement and hardly any of that potential was tapped into in what's starting to feel like a decade.
And if Apple had invested into a successor for Cocoa, there might be a larger gap between native apps and (Electron) web apps, leading to some lock-in. Instead most new stuff is not native and for good reasons (and I do dislike the way they don't adhere to Mac conventions, but still).
I think ultimately the problem is Tim Cook. He's too attached to Apple's stock price. I think that's the one metric that he believes rates his performance. But inertia is a bitch. Like in politics, the effects might hit hard only once he's out and it could be too late to fix by then.
If I think about how much this impacts the economy overall (i.e. make millions of knowledge workers a little bit less efficient) then I can only hope that I'll see more sophisticated organizational structures in my lifetime that prevent such erosion.