Probably because most of us don't think it's correct at all.

TUI apps aren't common anymore, which adds to the confusion as a lot of people didn't grow up with them and don't grasp the difference. A TUI app takes control of the terminal and redraws different parts of the screen to present a consistent, non-scrolling experience. If you've ever used a system where your interface was an IBM 3270 emulator (or better, an actual 3270 terminal), that's TUI. vi/vim and non-GUI Emacs are also TUI.

A CLI app just prints its output at the cursor and the output scrolls off the top of the screen as you go. The Bourne, Korn, Bourne Again, and C shells are all CLI, as are most REPLs and the majority of interactive non-GUI UNIX programs (including ed) these days.