Because a minimum viable GUI is way worse experience than a minimum viable TUI. Also GUIs take more skill in order to feel performant, which many companies do not possess (just look at various documentation webapps that take >100ms just to navigate between really simple mostly-text pages. Horrible).

Good GUIs with full keyboard functionality are definitely better than TUIs though. There's just no guarantee that some solo dev'd GUI for a brand new workflow can meet that standard.