But then the system started getting bigger. And after a while there were zillions of few-letter commands. And most mere mortals couldn't remember them. And the whole thing started looking completely incomprehensible. Well, it's the same kind of thing with mathematical notation, or any other kind of notation, for that matter.
People can handle a modest number of special forms and special characters.
Maybe a few tens of them. Kind of an alphabet's worth. But not more. And if you try to give them more, particularly all at once, they just become confused and put off. Well, one has to qualify that a bit.