The command line shell has that benefit of piping text between programs. TUIs are runnable from the command line shell. -- So you can get many of the benefits of a GUI (e.g. discoverability) while sticking close to the terminal where you're doing things.

If you're going to "run command, edit command, run command", performing the edits from the terminal you're running the commands in seems reasonable/intuitive. (In contrast, for tools like VSCode, I think it's more common for terminals to take up a fraction of the screen space rather than switching it to full screen. And then developers will say they need a huge monitor).

It also seems to be that keyboard-driven programs are more commonly TUI than GUI. e.g. magit or lazygit. Or lazydocker. Or k9s.