I wish more TUI designers would spend some time playing with Hercules and experiencing the old "mainframe" way of arranging interfaces. Those guys really knew what they were doing.
Fixed positions, shortcuts, tab-indexed, the order is usually smartly layed out. Zero latency. Very possible to learn how forms are organized and enter data with muscle memory. No stealing focus when you don't expect it.
Optimized for power users, which is something of a lost art nowadays. GUIs were good for discoverability for a while but increasingly I think they are neither great for power users nor for novices, just annoying and yanky.
With a 3270 if the mainframe takes a second to give you the next form, that's not a UX problem at all. If your character terminal takes a second per keypress, that's very painful and l a g g y.
But character terminals were much cheaper, worse is better, so it won out.