So why is the number 21 million so important? Is it a magical number or your religion?
The number is not important as if it can create value, altcoins including Bitcoin forks should have good value. In fact they are dead coins with no value. With failures and deads of Bitcoin forks, altcoins you can see the number fails to create value if there are no good fundamentals, strong hashrate, good decentralization, good developments.
Some altcoins try to set shorter havling cycle like one year or two years but fail to have good halving bull runs.
There are some insights about that number but only Satoshi Nakamoto knows why he used that number. He explained it in some of his emails.
How is the 21M bitcoin cap defined and enforced?It means you don't understand why Satoshi chose 21 million. Nevertheless, it doesn't bother you. But does it bother you that I chose 2.625 bitcoins as my bet in this game?