Most prominent metals have considerable industrial use, which makes those metals valuable, and makes them de facto backed in a big way (by the demand for them). Bitcoin has modest industrial/economic use, at present (and obviously other cryptos may present different advantages in that regard, given time).
You also can't physically wear Bitcoin and show off status, unlike Gold, Silver and Platinum.
If gold gets cheap enough people will use it in their wallpaper because humans have an insatiable demand for luxury goods. That will never change. It's why people still adorn themselves with sparkly rocks and shiny metals after 20,000 years of supposed evolution and refinement.
The store of value argument for Bitcoin is fully legitimate; as are the arguments for building potent economic uses on top of blockchains. There's no reason humans can't invent superior stores of value, and ever better transaction & contract systems. However, those various valued physical metals are not unbacked. Bitcoin is unbacked, and it can be replaced by other coins in the near future, coins that are technologically superior for storing value, and so on. The properties that we like metals for, industrially, make them difficult to replace in most cases; the demand - at an industrial minimum - will remain for a long time to come accordingly. And the human population keeps expanding (~80m per year), the odds are zero the next two billion people will suddenly stop having any interest in wearing/owning gold as a status symbol, and that puts an enormous demand factor under gold (on top of the fact that the median has gotten richer, so their demand for luxury goods has skyrocketed; see: China 1990-2020).
Try mining new sums of scarce metals, or any metals for that matter. Try inventing a new metal.
Now try cloning Bitcoin or Litecoin. Trivial, relatively speaking. There are thousands of bullshit crypto clones, and there will be thousands more to come. Bitcoin is temporarily special due to acceptance. There is little industrial demand under that fickleness however, which means Bitcoin can easily fall out of favor, exchanged for the next popular fad coin that people decide is the better way to store value (click, click, you just converted your Bitcoin over to the next more popular coin, byebye Bitcoin; now try that process with physical metals that you need for manufacturing purposes).