There's a marked difference between running a Twitter-like application that scales to even a few hundred thousand users, and one that is a global scale application.
You may find quickly that, network effects aside, you would find yourself crushed under the weight and unexpected bottlenecks of that network you desire.
Agreed entirely but not sure that's relevant in what I'm replying to.
> we are at the point where you can install an app, tell the agent you want something that works exactly the same and just let it run until it produces it
That won't produce a global-scale application infrastructure either, it'll just reproduce the functionality available to the user.
What keeps people in are network effects and some dark patterns like vendor lock-in and data unportability.