Hmm right now bitcoin I agree with you btc is indeed only used to exchange value, however I have to give a few props to bitcoin why it could be a good store of value.

First reason that comes to my mind is that the distribution and inflation is known and low. Unlike gold we are not certain how much gold there is left in the earth.

Transferring bitcoin right now is not expensive and even at the peak levels we had about $10 each transaction, is not bad considering that we can send btc to anywhere with an internet connection.

If btc were the only coin, I think it could become a currency, and thus a store of value, however btc is not the only coin, but given its popularity already and the promising atomic swaps etc, I can't say for sure.