Because it's all keyboard based. Depending on your field of work a good UI can be very different.

A few years ago I watched an account work through my companies numbers using their accounting software. It's entry method? A windows commander like tool. The menu options like add expense etc were all numbered. So he never left the numeric part of his keyboard.

The tool looked super old and obsolete but as soon as you see a power user use it, you see why.

I wasn't alive in the 70s, but I still prefer a terminal.

I can string together a complex series of text-related tasks far more effectively as a shell pipeline than I can by pointing and clicking in a UI. I can scale that sequence of tasks out to operate on every file on the filesystem if I want, or down to a single character in a single file.

Claude Code being a full-featured TUI is also helpful because I can quickly/easily use it remotely via SSH without having to deal with setting up X forwarding, VNC, Parsec, etc. The remote host doesn't even need to have a window manager. Sure, it'd be nice if it also had an elegant multi-page GUI so I could more easily drill into the actions its performing and make better use of my large screen to watch it do multi-agent things, but if I have to choose between the two, I prefer the TUI.

That said, I'd much rather use a GUI to do things that are actually visual/spatial in nature.

I don't mind a GUI (as long as it isn't an obnoxiously large ribbon or anything) - but if I'm doing work my input device is the keyboard. I don't want to interface with software through moving a mouse pointer when I can just tell it what to do with a few keystrokes.

It might be overcompensation. I think UI, UX and GUIs got better up until the 90s, and early 2000s, but then somewhere GUIs suddenly got a lot worse. So a modern CLI is better and more standardized than a modern GUI.

And some of us love to live in the 1970s with cheap non-HiDPI monitors (or maybe it's just me).