They are supposed to be clearing houses for people producing commodities and those wanting to use the commodities.
So, people could sell future production, or buy the stuff now, to be used in the future.
But, today they are rigged to the core.
SLV sells all the silver that is mined in a year, every single day.
There is no way they have even a fraction of the silver they say they do / should have in the vaults.
And the silver manipulators are using this to manipulate the price.