As the gold price of a $20 token falls, more people with gold are willing to convert it into tokens, and fewer people with money are willing to buy gold at that rate. As the gold price rises, the value of the token begins to exceed the value of the time spent accumulating the gold for some market participants and they stop selling their gold. Meanwhile, other people with cash are enticed to enter the market because of the high amount of gold they can get for their tokens.
Something to keep in mind as well is that this will make enchanting materials more valuable, since it is likely most players will now simply scrap their boe greens instead of getting them disenchanted. Also redundant dungeon/raid gear can be scrapped rather than traded to the (guild) enchanter in the run. Less stuff gets disenchanted, meaning there will be less ecnhanting materials, meaning their value will rise. All the more reason to DE rather than scrap as an ecnhanter.