Because the genie union lobbied and one that right. More wishes caused the genies to be overworked and fatigued. This lead to mistakes being made. Such as someone wanting 1 million bucks getting 1 million male deer instead of $1 million.
How come you can only ask a genie for just 3 wishes?
To keep the greed down a little. (Three wishes is a lot!)
Really 1 is all you need
They are unionized.
It's the way the "Myth" was written in "Arabian Nights".
Here is an interesting read regading Jinn, Djinn or Geneies.
http://www.giantglacier.com/the-origin-of-the-genie-in-the-lamp/
