A commodity always has a use by itself. If gold were not used as medium of exchange or storage of value it would still be useful because you can make useful things with it, such as electronics and jewelry.
Bitcoin does not have that property. If I were the only person in the world to have Bitcoins it would be useless, just as with any other currency.
Hmmmm - if you were the only one in the world to have gold, would it not be similarly worthless? One can derive aesthetic value from gold, but a computer nerd can similarly derive tech-geek aesthetic value from Bitcoins. Indeed, before BTC had a market price, people traded them because they are cool - there is an aesthetic property to Bitcoin as a thing, just like a shiny stone or metal.
And further, it is not true that Bitcoin has "no" value other than money. There are a few weird uses people have mentioned - a timestamp, a means of anonymous proof of various info, a distributed record keeper, and certainly others we haven't considered.
So while bitcoin's value may be due 99.999% to its usefulness as money, it has some tiny fraction of value beyond that. Does that not then satisfy your commodity definition? Let's remember too that gold's value is vastly due to its use as money and a store of value (which derives in turn from its usefulness as money). If jewelry and industry were the only uses of gold, it's price would be vastly lower, probably in the single digits of what it is now.
So what then is the fundamental difference that makes gold a commodity money, but not bitcoin? Both are commodity monies in my opinion, the former a physical commodity and the later a digital commodity.
This couldn't be more inline as to how I view the world.