Yep, you are right that 21M is the choice of Satoshi Nakamoto. Not only Bitcoin, every coin has a controlled of supply. If it was not controlled of supply it will lost it market value and balance. The reason of king in crypto world, other coin also followed bitcoin's. There are some coin in the market who have less then 3 Million of supply. But those coin can't  reach the price of bitcoin.  I love and hopefully about BTC.