It does seems niche at this point. One scenario I can see is where you want something more user friendly than pure CLI and where providing a web UI might be too risky for some reason. A TUI could allow users to SSH in to server somewhere and just have TUI app as their shell. It's a bit contrived I grant you that.

Personally I found Textual a little weird to use, but better than ncurses. Though it didn't really yield what I wanted. I like the old mainframe style TUI application, those already struck me as being wildly efficient.