

A good modern gui also presents itself in front of you. It directs your attention to important buttons/options. You don’t need any prior knowledge to know that a cog shaped button labeled settings will take you to settings. Good UIs are self explanatory. CLI are not.
To be able to use the terminal, you either need another person to tell you the necessary commands or search for a tutorial yourself, either online or somewhere else.
That’s not intuitive. It’s not too hard to learn, but you need to actively pursue learning how to do it. An average person doesn’t want to do that. An average person doesn’t even want to memorize more than one password. They should. But they won’t. Thus, password managers were created. And non technical minded people still don’t even use those.
You got to look at it from the point of view of someone who has no interest in knowing any more about their computer than how to turn it on, where to put their photos and how to open their browser and maybe an office suite. The kind of people that wouldn’t even update the system, if there wasn’t a notification asking for it. They’re not stupid. They just don’t care about computers and don’t want to spend any more mental power on them than necessary, the same way you wouldn’t want to think about manually keeping the timing of your car’s engine on point for the current conditions. You just want it to get you safely from A to B. Or maybe you do, but I assure you, most people wouldn’t.
The CLI is very much an enthusiast/professional tool. It isn‘t and it shouldn’t be the default in this day and age. Saying everyone should know how to use the CLI is like saying everyone should know how to use a DSLR camera instead of just relying on their phone’s or everyone should know how to drive a manual transmission car. Those are all great skills to have but most people just want a snapshot or a car that gets them from A to B safely. They don’t want to think about it. And most people just want a computer that gets out of their way. And why shouldn’t they have it?
And I’m not saying the terminal shouldn’t exist and that people shouldn’t be encouraged to learn about how it functions. But there should always be the option to completely avoid it. Because of you want mainstream adoption, you need to face the sad reality, that the Mainstream doesn’t want to look under the hood. And if you don’t want mainstream adoption, why?