Have you actually played these games? I put in some hours on Hitchhikers Guide, and It was anything but natural. Maybe once you get far enough in the game and learn the language that is effective it gets easier, but I never got there. You wake up in the dark and have to figure out how to even turn on the light. Then you have to do a series of actions in very specific order before you can get out of your bedroom.
Figuring it all out is part of the fun, but outside the context of a game it would be maddening.
As for Eliza, she mostly just repeats back the last thing you said as a question. “My dog has fleas.” “How does your dog having fleas make you feel?”
Which is why it's done that way. Other text-based games where the focus is not on puzzling out what to do next (like roleplaying MUDs) have a more strict and easily discoverable vocabulary.
This would be like saying using programming languages is terrible because Brainfuck is a terrible programming language.
Figuring it all out is part of the fun, but outside the context of a game it would be maddening.
As for Eliza, she mostly just repeats back the last thing you said as a question. “My dog has fleas.” “How does your dog having fleas make you feel?”