Because at the time I bought my iD the current retail one were not released yet, and I wasn't even aware of them.
But it's cool to choose your own design anyway. I like the "colorway" of the current vapor, but not the "design" : the black fingers aren't my cup of tea. I choose a full white upper instead, and a black sole. No regret, really
(watch a couple of pages back in this thread to see them)
About the price, yes it's a bit more expensive than retail, but again it's cool to make your own design and have a unique colorway. I could afford it some months ago, so I bought them.