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.
Edit history in JetBrains being on by default saved my bacon a few times over the years.