bitcoin is a shining thing.
Let's try to understand  why people like shining objects. I think is radically a form of comunication: jewels like wampum shells, are worn so you can see it from far. If you have a commodity which is visible from far an so is possible to desire it for somebody who looks, you'are just advertising for it. Maybe your advertising works becaus you are a powerful, violent king, but maybe advertising needs no testimonial. If you adveritse for a commlodity, this commodity gets  medium of exchange value. Bitcoin is an internet based viral advertising campaign for a commodity, so it's a very shining, visible from far object. That's why (given the two other proprieties of rareness and indestructibility ) it's a good store of value.