According to the Austrian School of economics, a thing has to be valuable or seen as a store of value before it can be used as a medium of exchange. This podcast has a great explanation of this: https://stephanlivera.com/episode/76/.

Why would you spend bitcoin if you didn't have to if you believed it’s going to be a lot more valuable 5 or 10 years from now?

Famously, a guy spent 10,000 BTC to buy two pizzas during the early days; that’s over $94 million USD at today's prices.