Vi is meant for old school and modern terminals. Ctrl+S or Ctrl+C had very particular purposes in software control flow. With Vi you can communicate via SSH on almost any unix file system. It’s basically a universal editor that doesn’t require a mouse or a lot of keys on a keyboard. You can get away with just a subset of the ASCII set.
So for one, it’s kind of like having a backwards compatible piece of software that exists on almost any system you might need to remotely control via a keyboard with no GUI.
For two, once you do learn how to use Vi/Vim/Emacs, you’ll be far faster at typing. It has several useful tricks for automating typing (faster copy/paste, copy/paste n-times, jump around lines/chars, go-to lines, search via Regex, etc.) which are particularly useful in a programming context.
Generally, it’s worth a developer spending at least a day or a week typing only in Vi for programming. Yes, you’ll be slow and clunky. But the moment you have to SSH into a server and make meaningful changes to a file, you’ll be happy you spent the time.