A stablecoin isn't a store of value. It's an instrument for holding pretend Fiat. It's a way for holders to pretend they are the Fed, and say "Now I have USD! You can have it. Just sell it back to someone else eventually because it's pretend."
It's an index basically, not an actual commodity.
(Except of course in the sense that Everything Is A Commodity in the crypto world.)
Eh, I wouldn't quite call it an index. While I agree that it isn't _actually_ 1USD (or whatever it is pegged to), it is backed by other assets (in the case of DAI today, it is backed by ETH) and the system is setup such that there should always be more ETH backing the DAI than necessary to make everyone whole.
It's an index basically, not an actual commodity.
(Except of course in the sense that Everything Is A Commodity in the crypto world.)