Just think about this:
Total humans: 7,360,837,156
That mean 0.002852 btc/human
but the total humans number is going up in the time. There is not enough btc for all.
that's why you can divide bitcoin into satoshies
Total bitcoins: 21,000,000
Total Satoshies: 2,100,000,000,000,000
Total humans: 7,360,837,156
That means 285293 Satoshi/human