Early software was often modal, but usability took a turn at some point, away from this style.
VI-based editors are total enigmas — they’re the only real surviving members of that order of software.
Modes are a no-no in usability and interaction design because we humans are fickle mammals who cannot be trusted to remember what mode the application is in.
If you think you are in one “mode” when you are actually in another, then all sorts of badness can ensue. What you believe to be a series of harmless keystrokes can (in the wrong mode) cause unlimited catastrophe. This is known as a “mode error”.
To learn more, search for the term “modeless” (and “usability”)
As mentioned in the comments below, a Modal interface in the hands of an experienced and non-fickle person can be extremely efficient.