Thanks for looking that up! It makes sense, of course - the line starts to drop in 1984, with the release of the Macintosh, and hits a trough around the launch of Windows 95.

It's not a term I recall hearing at all when I started using computers in the mid-'80s - all that mattered back then was "shiny new GUI, or the clunky old thing?" I really thought it was a retroneologism when I first heard it, maybe twenty years ago.

I don't think that search is very valid - the TUI group travel companies are likely much more mentioned than Terminal User Interface. They are pretty big around the world and have an airline, cruises, hotels etc.