In those aspects of UX, voice interfaces have the same drawbacks as console apps when compared to a good GUI.
Also, they have to work within the "bandwidth bottleneck" of audio - just imagine a phone system that tells you all the options you have, "Press 1 for something, Press 2 for another thing..." - they are so annoying because they are slow and inherently linear; a GUI can show the same options all at once, and you can read it much faster than listen to them.
So NLP as such is not dramatically more user-friendly unless it is at the "do what I mean" level which likely requries full human-level general artificial intelligence; before that it's just a voice equivalent of a console app, sharing all the problems of discoverability and needing to remember what the system can do and how should it be invoked.
They're even slower now because the brain trust decided adding voice control to the phone menu system was a great idea. So before, it said "For prescription refills, press 1." Now I have to wait for "For prescription refills, press 1, or say prescription refills." How on earth does that improve anything? I can just as easily press 1 as I can say a word, and when I press 1, there is a near 100% chance that the computer on the other end will understand my command.
Some phone menu voice automation are even worse. "Tell me what you want! <silence>" Then you say something, and it says "I didn't recognize that. Please tell me what you want!" Then it fails again and says "I didn't recognize that. For prescription refills, press 1, or say prescription refills..." Oh great so there was a menu? Why did you waste my time earlier?
Voice is just a terrible, low-fidelity, low-bandwidth way of commanding a computer. You might as well have handwriting input while you're at it: You write what you want on a piece of paper, and hold it up to the camera and the computer tries to figure out what you wrote. Just as silly.
So, I would rarely say something when I could push a button, but when using a smartphone on a call, it's not always easy or obvious how to push a button. Some people may have mobility issues making it hard to push a button, or be on speaker phone far away from the buttons. Or, maybe they haven't updated their telephone equipment in 50 years, and only have a rotary dial. Or, maybe on a terrible VoIP system that can't manage to get the tones through.
There's probably some way to clean up the script.
"(Please listen carefully, as our options have changed.) Please choose from the following options: Say prescription refills or press 1; say insurance denied or press 2; say referral to veterinary care or press 3"
I could get behind voice interfaces for more things if the commands words were documented, clear, and consistent, and the damn things worked. Until then, buttons seem good to me.
Ironically I used to love me some graffiti on PalmOS and Google Handwriting Input on my Droid 2, but I agree with the spirit of your comment.
"Welcome to FedEx. [... blah blah blah ...] Tell me what I can help you with today."
"a package"
I mean, what the hell else can you help me with today anyway?
foo --<tab>
You're now present with a list of options and depending on your config, the man page one liner descriptionsGUIs are for discovery, CLIs are for power via composability, voice/NLP assistants are for convenience.
Was it? Even if you discard stuff like tmux as already a GUI, you can still send whatever is running at the moment to the background with CTRL-Z and typing "bg" on any modern Unix system. "jobs" will then list all your processes, and "fg <ID>" will bring it to the foreground. I am sure this functionality predates most modern GUIs.
You may be thinking of DOS, which yes had almost no multitasking ability available.
However there were multiple timesharing operating systems that existed before the PC and GUIs, Unix being the most famous and still around.
Multitasking is quite possible on a Linux console for example. It has 5 or more consoles, each handling different users, each being able to be split via screen/tmux. Each shell can run jobs in the background as well.