It’s somewhat important for privacy reasons that the feature is opt-in. I don’t know if that’s the reason historically, but I wouldn’t want a text editor to persistently store a copy of everything I type without my consent. It’s almost like a keylogger.

Making privacy-sensitive features opt-in is a form of duty of care as well, to avert harm from the user.

I prefer persistent undo being off. I like being able to hold down u and revert to exactly how the file was before I opened it. (Maybe there's a better way to do this?) With persistent undo on, it just keeps going and going. And if I need long term source control, that's what git is for. With persistent undo off, it's like opening the file creates a checkpoint that I can get back to easily.

Emacs and Vim are basically like that.

They have very vocal and entrenched users so that practically no defaults can be changed lest the single Amiga user will start a huge uproar.

And since they don't really have a BDFL or commercial pressure, they can be super detached even from standards or expectations that appeared 40 years ago.

Neovim was basically a reaction to that, for Vim, where they updated defaults to stuff basically every Unix editor since 2005 has.