Sometimes your system doesn’t have a graphical session, like a raspberry pi with no x server running, or a cloud compute instance I’m ssh’ed into, or a docker image running on my laptop. Sometimes your system doesn’t have a (particularly usable) text system, like a work computer that disables the terminal or a family member’s MacBook who doesn’t have the time or space to install XCode terminal utilities to be able to use things like brew install.

My point is that it’s not a given that having one means you have the other.

TUIs are wonderful for the first case.