If there was a security that perfectly tracked the price of a commodity, why would anyone invest in the commodity?
The commodity, after all, has actual costs (such as storage, insurance, and transport.)
That is, if you were to buy 10,000 barrels of oil, there will be s cost for you to store it.
If that cost was absent from the mythical intangible instrument that perfectly tracked oil, why would you or anyone else buy the real thing for investment purposes?
Buying a 'synthetic' commodity -- that is, and instruments thst strives to match the commodities price -- will force you to give up something; maybe the amplitude of the swings in price, or a hefty chunk for transaction costs, or other such things. (I believe 'backwardation' and 'contsngo' are the terms for the factors that prevent a collection of future contract perfectly tracking the percentage delta spot price of the underlying commodity.)