You may state it has failed from your perspective, but it is actually used quite often.
It's just not used for the things you're buying. You don't need BTC to buy stuff at the store. The State enforces dollar legitimacy.
So what's it good for? Anything the State does not recognize. In this realm, BTC and siblings like XMR are vigorously exchanged. Surely your imagination can fill in the details. :)
Most uses of Bitcoin for actual transactions would not exist at all in an ideal world, with perhaps some minor exceptions (e.g. protecting money from tyrannical regimes).
It's just not used for the things you're buying. You don't need BTC to buy stuff at the store. The State enforces dollar legitimacy.
So what's it good for? Anything the State does not recognize. In this realm, BTC and siblings like XMR are vigorously exchanged. Surely your imagination can fill in the details. :)