I think a lot of Gold traders also see the threat of investing into something where a centralized authority holds they key to your wealth. This is not the same with Bitcoin, when you invest in Bitcoin, you hold the key. <The Private key>
They also realized over the years that Gold cartels are manipulating the Gold price too and many people believe that the actual Gold that should be stored in some vault, might not be there anymore.
And there is this scheme where they take out a portion of the gold inside a ingot and replace it with a cheaper metal that weights almost the same, covering any traces with actual gold. How are you going to inspect each and every ingot bar? You'd need to melt them and mint them again.
Also, someone will find gold in an asteroid someday... Gold is a nice metal, but way overpriced. Rust-less metal things like a fence as opposed to useless rings or jewelry, for example. Anyone living near the sea could use it in many more useful ways if it wasn't so darn expensive.
Before Europe "discovered" the Americas, South America actually had more gold than iron. Guess which one was considered more valuable? But their view of the world was limited to their lands, how were they going to know that worldwide gold was the scarce one. Of course most was pillaged and taken to Europe, made into useless jewelry or boring ingots to be "stored" and never seen by anyone ever again...
