Because it’s too complex and not worth the effort. Most users will not care about or perceive the benefit. If they delegate that responsibility to Google via Electron, they can focus on features/bug fixes that move the needle.
Especially since users do prefer a native experience and having their RAM conserved.
I hate Electron apps with a passion, but I can understand why the AI companies are using it.
Once the initial port is done, keeping platforms in sync is fast. Not to mention that a harness that would automate this would be valuable.
I run codex on an old rpi, it eats 190M of ram for what essentially is a telnet client.