There are 4 components to a language. Speaking, understanding, reading and writing. Now to get through life you really need a lot of speaking and understanding and just a little of reading and writing. So why learn reading and writing past elementary school I believe is your question.
I am currently tutoring a person in college who is taking a course with some math. Although she struggles a bit with the math, she cannot understand what her textbook is saying even though she knows each individual word. Now this is a college textbook and I guess they could have written it in plainer language that everyone could understand. Problem is that she would not know the vocabulary for her course and probably her job. Also, the book would be 3 times as thick because of all the extra words to make everyone understand, which would make it 1300 pages or so which would make it more expensive.
I have helped several people with their income tax forms because they can't understand the language that is usd and can't understand the directions to fill out the form. Now if you don't mind paying an accountant every year, that's fine. I save about $300 a year because I can read and interpret the laws governing the tax returns.
Then there is all the fine literature and poetry that you'd be missing. Some authors are extremely hard to read while others are relatively easy. These works of fiction all have a point, or several points they wanted to emphasize. Why did this character react this way? How would you have handled things differently? Do you think that what the character did was justified? Right or wrong?
Fiction like this is there to make you become more self-aware. Many, if not most, people rarely take the time to look at themselves and ask things like why do I think like that? Why do I react like that? Why am I SO angry instead of just upset? I had the problem when I was young...why am I afraid to talk to ANYONE......ridiculously shy. Did you ever read a book and find part of yourself in a character ..... like Catcher in the rye.....Romeo and Juliet.....If you said yes, and I'm sure you did, then you became a little more self aware AND maybe will start understanding how others think and why they act as they do.
And then there's non-fiction. I bought a book for one of my friend's 25 year old son on drug addiction. When you're unable to pay for counseling and unwilling to go to places like Alcoholics Anonymous or Narcotics Anonymous, reading a book on the subject might help you with some insight on how to stay clean. I read it 3 times so that I would have a better understanding of how to deal with him and he and I started reading it together, since he wouldn't do it himself, andwe made through the first chapter......almost. He read a little to me but he couldn't understand what he was reading....by the way, he dropped out of HS at the beginning of 9th. Since I've known this kid, he's been in and out of jail 3 times, comes out drug free, and within a month, is back to where he was. Try reading the book with me, I offer....He's about to go back to Jail.
Have you had enough yet? I have lots more to say.