Why ??

It’s possible that Satoshi simply wanted to make sure that Bitcoin couldn't be 'inflationary'. By having a fixed supply, there isn’t risk of inflation eroding the value of Bitcoin over time.

The '21 million' figure is a result of the way the Bitcoin algorithm works.

When the 21 millionth BTC is mined, that will be the maximum number of Bitcoins that can ever exist.. nostr:note12fhc354e9ewq7xvxsc0k6aqm8f4z2l8ej3gx3yt28ex9f4e6e74sttarrw