You are thinking about it wrong. there are 21 million whole bitcoins but also there is 8 decimals after the 1 whole bitcoin. which means there are 2,100,000,000,000,000 satoshi available and if you think about it, that amount is more than enough for the number of people who might be interested in bitcoin and want to use it. it will never be every single person on earth so it is enough. and with the value of bitcoin rising with more adoption, 1 satoshi will have a meaningful value. currently at $0.00014
The time is coming when people would be using the term satoshi for Bitcoin when its price has already reached by the millions. The number of possible Bitcoin is already fixed at 21 Million and with the way it is set-up it is 100% impossible to add more to that figure which can be the big reason why due to the increasing demand for the coin its price is really skyrocketing to the moon (or is it the stars?). Maybe OP is concerned that a time is coming when there can be a big shortage of Bitcoin, that exchanges would be drying up of Bitcoin to sell to possible buyers. Well, that scenario may not be happening at all due to the open dynamics of the market. There would always be sellers and buyers.