Blizzard added the new pet which can be bought for € and sold at the AH for in-game gold.
All players who were serious about buying the pet to sell it for gold, knew that the prices would drop over time. That's why all these people had to be fast. That's why they had to buy lots of pets now and sell them as fast as possible. Which is exactly what they did. Which leads to prices dropping even faster.
At some point the AH price will have dropped to a point that buying gold from gold sellers and then buying the pet in the AH is cheaper in €-terms than buying the pet from Blizzard ...
In the past, Blizzard could sell pets only to those players who were willing to pay the price. Blizzard could reduce this price over time to sell more pets, but that would reduce their profit as well. With the new system, the players who would buy the pet only for a lower price than the one Blizzard asks, simply have to wait until the price in the AH dropped enough. Then they buy the gold from gold sellers and buy the pet.
- Blizzard, because they make the full price on all pets, regardless of whether the final customer actually wanted to pay the €-price.
- Gold sellers, as players will buy gold to buy the pet, because this is eventually cheaper than buying the pet directly.
- The players who want the pet, but didn't want to pay the original price at the Blizzard store. But only if they are willing to buy gold from gold sellers.
- The players who want to buy a pet for gold they earned in-game. There would have been easier ways to satisfy these players, of course.
- The players who think that they can make a lot of gold by buying the pet. Unless they are very fast, they will find out that it would have been more effective to buy gold from gold sellers.
- Players who don't like RMT.