A Big Mac may cost $5 now, $10 in the future. But I would like a Big Mac Coin that lets me exchange it for one Big Mac in any time in the future. It has value as long as McDonald's exist and is willing to accept the coins, which is better than you can say of most crypto.
It may be a different sized burger, it may have somewhat different ingredients. Even our "classic coke" is nothing like the original coke. But this is what I'd expect from branded stablecoins.