Compare gold to the other elements on the periodic table as a medium to store value and you'll see why it is used for this task.
It is non toxic, it can be easily held and transported, it is non reactive (it won't rust or combust), it is relatively rare, it is dense (a lot of gold fills a small space) and, well like others have said, it's shiny. It can be easily moulded and forgotten about for millennia and still be the same way it was last used (look at Viking hordes as an example) few other things can do this, maybe diamonds? But they can not be recombined again like gold
Imagine if some one held the US feet to the fire about promoting democracy and providing defensive coverage to polls. I mean Trump has no shame and neither do his cheer leaders, but do the people still want to feel pride?