I've got a bit of a different on it... It's because TUIs do lend themselves better to automation (it's been mentioned in the thread) and, most importantly, it's because there's less cognitive dissonance between a TUI and how it typically operates and... The way AIs are using command line tools / the terminal (or a REPL, for those using agents hooked to a REPL).

In a way AI agents are validating what us old-timers always knew: the CLI and TUIs is the most powerful way. And AI tools didn't choose the most common dev environment: devs using fat IDEs (and btw I was already using IntelliJ IDEA back when some people were still arguing NetBeans was better than IntelliJ) are way more common than those piping Unix commands to achieve even simple tasks. Instead AI tools did choose the most powerful way to work: and that's piping terminal commands and SSH/tmux/TUIs.

When the tool itself, like Claude Code CLI, is immediately showing the outputs of piped Unix commands and allowing to run commands from a prompt and is, itself, a TUI, it's validating that it's an extremely powerful way to work.

A Claude Code CLI (or similar) TUI in a tmux session is something quite powerful.

Then you combine that with the fact that techs like LSP and tree-sitter did at least partially commodotize the IDE and suddenly TUIs (or things very close to it, like GUI Emacs: which can do graphics but is still mostly used as a TUI tool) do look very appealing.

Magit is considered by many --even non Emacs user-- as the best Git interface ever. It's text, text and more text.

My life is terminals (text), Git and Magit (text), Emacs (GUI but basically text), SSH (text), tmux (text), many text things I forgot and now TUI harnesses.

If you're modelizing in Blender or editing movies or creating movies, a GUI makes sense. But if you write code, which is text, all you need is text, text and more text.

TUIs are making a comeback because it is all text and AI agents are proof of that.