the number of monetary units has no effect on total wealth at all. it simply represents the amount of wealth that exists. ideally the number of units would track with human productivity and buying power per unit would remain stable. but there's no decentralized way to do that. and a hard cap means permanent deflationary conditions, which is a very bad design as it incentivizes hodling as much as possible. so we pick a constant that generally tracks with historical economic growth. it worked for gold for thousands of years. "only 21 million" is just a meme. and memes make bad monetarily policy.