Earlier quoted context omitted.
Back in the old days, the primary users of many mainframe UIs were the data entry team (almost universally female). Sitting in large offices with rows of desks and a huge clock on the front wall, they weren't interacting with customers, they were transcribing from sales sheets, order forms, application forms, etc. prepared by someone else. There was no great need for user friendliness, because the only users were in…
Mice are the problem, not the rest of the GUI. Keyboards are just faster once you learn them.
In a traditional TUI you can type at full speed and the system will process the keystrokes as it is able, with no keystrokes being lost. If a keystroke calls up a new screen, then the very next keystroke will apply to that screen. Competent users could be several screens ahead of the computer, because the system doesn't make them wait for the UI to appear before accepting the keystrokes that will apply to that UI.