In my opinion, Bitcoin is a store of value, not a currency.
Bitcoin has two functions, as a digital asset (investment) and a digital currency (payment tool).
There is no problem with those two functions of Bitcoin. It is surely your right to use it for investment or for payment tool, both are possible and worth. If you think it is not a currency, you are wrong. In the fact, Bitcoin is already used as a payment tool. Don't deny the fact, mate!!
There may be cryptocurrencies becoming legal tender, but not now, volatility and supply and demand need to be considered.
Why not? When do you think the right time?
Sooner or later, Bitcoin deserves to be a legal tender. I think El Salvador already showed us the potential of Bitcoin to be legal tender. This country has no doubt to begin Bitcoin as a legal tender. Now, some countries already consider following it as well.