It is estimated that more than 95% of the total potential supply of Bitcoin has already been mined, yet only 5% of the world's population holds Bitcoin worth at least $1.
A question for everyone: what will happen when 10% of the world's population shows an interest in acquiring it?
That's where the principle of demand and supply comes into play.
Bitcoin is already limited in supply, scarcity with increase alot when all the bitcoin is minted and if in the future a large percentage of the world requires Bitcoin, it will drive it's price.
Don't think for once that there will be no more bitcoin for you to buy. Because there will definitely be it's called circulation.
Bitcoin will then continue to move from hands to hand, and this will continue to increase it's value.
You might think that everyone will hold, but that's not even true. Some investors just want to invest, make profits and sell off at a higher price. They are not into holding on a long term and this is going to keep circulation intact.