For scarcity reason since Satoshi want Bitcoin to be valuable same as gold.

Its for trust for transparency and anti inflationary model which if he choose choose to release a unlimited supply there's provably huge problem on its sustainability. That's why I can say that Satoshi is really smart and know how to make his creation became more successful then also valuable to people in the world.

If you want to know more about Bitcoin you can read lots of information here https://bitcoin.org/en/bitcoin-paper