It's built in to the Mercurial CLI, whereas tab autocomplete is an additional feature to the user's shell. Thus, by default, every user will have access to the Mercurial shortnames, while only users with autocomplete enabled in their shell (or with autocomplete available for their shell) will have the autocomplete available.
Also, autocomplete is still an additional keypress...
What you're saying is technically accurate to the intended definition and purpose of science, but if you're seriously asking why these people didn't question or contradict, I'm not sure where you've been for the last several years. So many pandemic response items, in particular, have been "Trust the science"/"Follow the science", and any questions or possible alternatives to the prescribed Method Of Treatment are not only dismissed, but actively persecuted.
The idea OP is working to combat or disprove, though, is not that "People can succeed without effort". Rather, they are working to prove that software development is a skill which can be learned by most/all people, and not some highly intellectual undertaking out of reach to all but the most mentally elite.
Or...
Knowledge is understanding that ketchup is tomato jelly. Wisdom is refraining from putting it on your peanut butter and jelly sandwich.