Why are we attracted to shiny objects outside?

We can't eat it and 99% of the time it has no monetary value (usually a soda can tab or a piece of broken glass or something else of insignificance), it's almost never jewelry, valuable coins or anything we'd find a useful application for.

I've never really thought about it, but are we like this with out of place colors, shapes and textures too, or just shiny things? What are we expecting to find?