Gold, for all intents and purposes, is also "backed by nothing".
If gold wasn't used as a store of value its value would be very maybe a hundredth of what it is now: Gold-plated jewelry in our modern era is essentially indistinguishable (even at the level of a physics lab using scales/xrays/etc if need be) from solid gold jewelry. Gold, for all intents and purposes, is also "backed by nothing". << again has almost nothing to do with Bitcoin being back by nothing. Gold is the item of value it doesn't need to be backed, it is the back'er.
Bitcoin is essentially the same as it replicates the same properties of gold while having a more predictable supply and features that allow it to be used more commonly as a currency, unlike gold.