Market manipulation is part of money making, China and others had large reserves of rubber, they cutback on buying.
Reserves shrank and price falls, it's a buyers market, drop the price and then buy cheap.
Good business sense, but un vulcanized rubber has a 2 year shelf life, so you can only play the game short term.
No business or country wants a shortage of reserve commodities, be it oil, steel or rubber, big player stuff.
We just have to live in a world that small people have little say, tomorrow things change. China goes cold war they stockpile, NATO and Russia same, world economy booms, same again.
Life, Jim