IMO, before 2008, banks loaned out money to pump up house price, and eventually those houses did not worth that much because of low cost and oversupply, and then they can not dump to consumer since the consumer would just default. So they have to dump to FED (MBS)
However, once those houses were sold to FED, they are holding lots of fiat money and those money have no where to go due to low return in the general economy. And they dare not to let those money into economy either, since that will trigger heavy inflation. So they decided to send those money oversea and pump the raw material and commodities, petroleum etc...
Now after QE stopped, commercial banks' large income (sell houses to FED) also stopped, they ran low on USD, so they have to reduce the commodity purchase at other places. This affected all the industry raw material and commodities, not only petroleum
Unlike last time, FED have no interest in supporting the price of these things, so it is very likely they will fall sharply until below the manufacturing cost (market can be irrational much longer than you can imagine), just like bitcoin did. Since a high price will create investment demand, when price crashed, many investments will fail, just like blindly built mining farms during the bitcoin price rally last year
It is all pump and dump when fiat money can be created out of nothing and directed to any thing that have value. And the sad thing is that people blindly use fiat money to measure value. What a freaky era we are living in, just like Austrian economists predicted, when money supply can be manipulated, it will always give a wrong signal of market supply and demand, thus create waves of wrong investment and redistribute wealth in the process. It is very likely the next pump and dump target is bitcoin, be prepared