As someone who works on a very GUI-centric OS (i.e. Mac), TUIs just don't integrate very well with the rest of the non-Terminal ecosystem.

They don't support standard GUI shortcuts. They don't support drag-and-drop. I can't double-click a file and have it open in a TUI. They don't integrate with spotlight metadata. They don't ship document icons. They have terrible support for accessibility APIs. And so on...

It's somewhat an issue with Linux as well.

Ctrl c does 2 completely different things. Terminology is different. Etc.

Problem is. Terminal applications standardised in the 70s. Guis in the 90s. Although that's being undone by web apps, and the influence of touch screens.