Ah right, it’s free software. There is no milkshake, only people with similar ideology contributing to a common cause.
1. Ceteris paribus, the developers won't be able to deliver new features as quickly, nor fix bugs as reliably, as projects which use AI.
2. They will be unable to attract and retain a large number of developers because there are just not that many people who code by hand anymore; rational people can see the massive productivity gains AI gives you
And of course, the user base will be siphoned off entirely to the fork which gets more and better updates, leaving "Human Emacs", if it ever comes into existence, a largely abandoned project within short order. This has already happened, albeit not in the AI context: in the mid-90s, XEmacs was leaps and bounds ahead of GNU, and today it's pretty much abandonware.
There's just no future in coding by hand. It's like trying to keep punched cards alive. Forget it. It's done. Pencils down. Embrace the future, or face irrelevance.