why is founder edition gtx 1080 more expensive?

Solution
Simple answer: People want an in-house built card that is a near silent blower style. (See Asus Turbo 970 reviews on newegg for the opposite).

Complicated answer: Nvidia coolers have always been desirable, so they can charge more for them. This also opens up lower pricing for competing vendors. Since Nvidia makes everything and doesn't pay itself a licensing fee for the tech, it could technically gouge out it's partners by lowering the price so low, that they can't compete unless they operate at a loss. So Nvidia keeps it's own parts high, and the partners still get to make profit. Now, that's not to say that they won't offer cards that are the same price as Nvidia's, they'll probably have more features and a higher clock, but you...
Simple answer: People want an in-house built card that is a near silent blower style. (See Asus Turbo 970 reviews on newegg for the opposite).

Complicated answer: Nvidia coolers have always been desirable, so they can charge more for them. This also opens up lower pricing for competing vendors. Since Nvidia makes everything and doesn't pay itself a licensing fee for the tech, it could technically gouge out it's partners by lowering the price so low, that they can't compete unless they operate at a loss. So Nvidia keeps it's own parts high, and the partners still get to make profit. Now, that's not to say that they won't offer cards that are the same price as Nvidia's, they'll probably have more features and a higher clock, but you should be able to get a standard clock speed card from Zotac for $100 less.
 
Solution
as skynetrising said.. early adopter premium..
and some other reasons like ..
thats the original formula of the 10 series..
that is how the card is originally meant to be used..
they consider that design to be the best design ..
the main reason might be that they dont want compete with board partners..
but honestly there are not many reasons to consider a founders card!
board partners like evga , msi etc will give it better cooling better OC better system application at a cheaper price..
unless you want to be an early adopter(this founders edition will be available through its life time so theres not much advantage anyway) i would wait for board partner options!!