It rebounding and crashing by hundreds in value like a meth head on caffeinated cocaine laced with LSD is what doesn't make it a currency.
No one wants a shit currency where one day a donut costs 1000 and the next 2000 and on the weekend it's either 599 or 3999.
That's why it's at best a speculative asset, except it's dumber than that because it's intangible. It's like the long term stupidity of fiat mixed with insane instability, all while using way more resources.