macOS exposes a lot of affordances to code/xrpc/services/etc that Shortcuts (and previously automator) used. They let you do basically anything you'd want on macOS programmatically, without going through accessibility frameworks, code signing and sand-boxing issues. iOS as well to some extent.

Presumably if OpenAI is dog-walked/locked out of these by Apple at some point, they would be stuck in the Chrome/Chromebook feature jail. My guess is this gives OpenAI a team to put in charge to give them a chance to wedge themselves into the OS before Apple changes their mind or puts scare-box dialogs everywhere.

Either that or there's nothing so complicated and OpenAI just wants to re-build this stack inside ChatGPT as quickly and well as they can.