Every single one of us on this forum right now are millionaires. The amount of Bitcoins we own right now is worth millions by 2140. The truth is that none of us would be able to spend the money on goods and services since 2140 is outside our life expectancy.
Even if we can live till 2140, but my question is can we keep our bitcoins till then? People are planning to sell bitcoin when bitcoin reaches $100k or $1 million in the future to escape from miserable life and enjoy life. And holding bitcoin for 4 years or 10 years is an extremely difficult challenge and not too many people can do it, so never think about holding bitcoin for 50 years or 100 years. That sounds funny.
Also, there is no guarantee that bitcoin can exist or still be used until then, look at the development of technology and I believe that in the future something better than bitcoin will be created go out.