Or even much sooner, when there's only 2 or 10 left to mine?
I guess because by that point the price of electricity to mine will become so huge no one will want to, and the psychological deterrent of buying insanely expensive coins. I can see it crashing because people will think "well there's no more supply, and those that have it won't relinquish it." I don't know there's an economic term for it, something like fatigue.
But also like... Right now we're still in the early stages, and Bitcoin isn't really being used as a currency. But people are buying right now because they think that, one day in the future, it will be used as currency in every day life. But everyone is just a hodler because of game theory and the price going into the millions in the future, then... It'll never be used as currency, because nobody will ever ever want to spend their sats. And so it's like... If it's never actually used as currency, and everybody realizes that everybody else is just hodling, then that's when it crashes. And all it will take is some giant that holds thousands of Bitcoin to sell out before everyone else does, and it'll crash and become worthless. Because right now crashes are fine because everyone still believes in it (like any currency, it only has value because people believe it does). Like, does that make sense?
People don't use gold in every day transactions, they haven't for hundreds of years basically. Fiat was developed using gold against it bc gold wasn't easily transportable, etc etc. If Bitcoin is digital gold, except with the benefit being transportable and divisible, then... Why would anyone ever spend it, if it's always going to be worth more in the future?
Or maybe the price will stabilize once the last coin is mined, 100 years from now, and then that's when it will finally be used as currency.