Well, its
1) Not packaged
2) A head swap between 2 ponies
3) Easy to fake
4) Abundant
On the other hand they were from a Chinese seller originally, who does tend to have factory rejects, runs of ponies that weren't sold, etc.
I think there is a little creative combining here by someone in China, because there are a similar amount of DJs with Rarity's head. There is no real answer to your question, but I am guessing that the individual pieces of the pony are legit, but she was not assembled in the factory. Maybe someone got a hold of rejected parts and put them together like this.