These are powerful pieces of software which massively benefit from native code doing processor/GPU intensive tasks. Totally different use-case.

Slack is literally just a fancy messaging app.

Games feel like a separate edge case. One of the most common complaints about cross-platform apps is they don't "feel native" or adhere to platform UX expectations. With games, there's an expectation they'll provide their own wholly own UI that doesn't match an existing commercial OS.

Also, video games aren't generally expected to be accessible to blind people via screen readers. If you develop a cross-platform app with a custom UI, it's going to have zero accessibility unless you implement each platform's accessibility API.

Yes, game devs already put in the effort of providing their own UI stack, and port that to every OS.

If most Electron apps were built as "games", i.e. providing their own UI via DirectX/OpenGL/Metal etc., I wonder if they might still be more efficient and less bloated than Electron apps are now.