Because COMEX sets the price and prints 100, 200, 500, 1000 pieces of paper they call "silver" for every oz of real silver. We could make oil/gas as cheap as want too—we'll just print a bazillion pieces of paper and call them gallons of gas. Oh wait, people expect their gas delivered in physical form so they can use it in their cars and trucks. A WHOLE LOT of people out there who THINK they own silver are about to get a VERY rude awakening one of these days.
When siilver goes to what it's worth, I can't even imagine what the world is going to look like, but it's gonna be an ugly transition. Don't toss any of your old puters or cell phones quite yet… landfills are gonna turn into the next mining boom.