They were not foiled by market forces, but by insiders changing the rules on the exchange (after taking up short positions for themselves). Here's an excerpt from an editorial posted on gold-eagle.com:
A similar thing happened in 1980 with the Hunt brothers. They [the exchange] basically changed the rules, and said their could be no more buying of silver...period. You couldn't buy it on the future's exchange. There could only be sales. When they closed the market down and reopened it, and only selling existed, well, as I stated in earlier in the show, when you have more sellers than buyers, the price goes down