With the dramatic fluctuation of BTC, why would anyone use it for everyday purchases?

"Visa announced plans to activate Bitcoin payments for 70 million merchants", "Tesla to accept Bitcoin in the near future", etc…

Maybe I'm missing it, but why would I use it for everyday purchases rather than HODLing or trading? The same amount of Bitcoin that would have been a down payment on a Tesla, would have bought one outright less than a year later.

2020: down payment on a car.
2021: down payment on a house.

What am I not understanding?