I'm sorry, I'm not here to teach basic economic theory.
Sources are plentiful and Google is your friend, if you really are interested, it is very easy to find material in abundance.
The ultra-short version for the interested reader is that disposable income is what drives progress - economic, technical, social. If everyone is barely scraping by and needs all his money for essentials, there's nothing left to pay artists, inventors, etc.
The ultra-wealthy do drive some of this and for most of history, they did. But a middle class, where lots of people have disposable income, drives so much more and desires so much more diversity that more paths are explored in parallel.
The mechanism, just so nobody can complain about me not answering the question, is called "investment". And while, again, the ultra-rich do that as well, there is more diversity and dynamics in the system the more people are involved.
Go through the list of Fortune 500 companies and remove every company that would not survive if the options were reduced to selling to the super-rich only, or selling life-essentials only (food - essential food, not sweets or luxury wines; clothes - but not fashion, just basic clothes; etc.).
You'll end up with a very, very short list. I'd be surprised if you had a Fortune 50 after this.