Why? You don't have to use Electron for everything, you can integrate using whatever language you want and some RPC, like Keybase did.

And that's still more involved (and slower) than "just use this function that desktop vendors helpfully provided for the purpose".

That one part yes, but if you can build most of your application cross-platform and only do certain things with "native" solutions you might get better bang for the buck. Discord and VS Code comes to mind.

Fair enough, but I expect browser integration and so forth to be done via the backend, which is rust, so native.

Rust is hardly a "desktop-native" language. I expect it will have to jump through all sorts of hoops to interface with the Obj-C underpinnings of MacOS desktop libraries.

Regardless, even if the backend were pure Obj-C, the point is still that now you have a UI stack and a backend stack, instead of a single desktop-native stack, and you have to manage their communications. But I guess the money they save by not managing desktop-specific codebases eventually adds up...