Blockchain is the ledger and mechanism/architecture. Currency is an object on top of it.
Anything can hold value. Value is subjective. People could store their value in the bank as us dollars, but they have no savings interest and inflation most certainly will destroy its value, or even in 2008 in Greece, govt can just take money out of your bank account.
So then... why is BTC so subjectively valuable? Well, govt can’t do that. You can travel anywhere with nothing and just remember those 12-24 words. That is a very powerful thing. To know it cant be inflated and it can't be stolen. It is fungible no matter where you are.