Currently, BTC is only used as a store of value,
No, Store of value is "the function of an asset that can be saved, retrieved and exchanged at a later time, and be predictably useful when retrieved. More generally, a store of value is anything that retains purchasing power into the future."
[1]This leads us to the following qualities: durable, easy to transport and have a stable price.
cryptocurrencies fail to be stable coins because of random fluctuations in their price(Decentralization).
its
Store-
Of-
Value
How do we expect cryptocurrencies to be adopted as valid payment methods when everyone is really using them as investment stocks?
The mistake of saying that these currencies are tools to invest(investment stocks)