Why is there no blue food?!
Answers: it's typically not a very appetizing color. Also those chemicals that produce blue colors in nature tend to be metal salts which, in quantities large enough to produce visible color, would be poisonous.
There is. Blue berries, and bluebery PIE!
As far as food companies think, most people don't think blue food is "cool". Get millions of people to write letters asking food companies to produce blue food, and behold, blue food will go onto the market.
P.S. You can make your own food blue with blue food coloring :-)
P.P.S. Some blueberries actually are blue (but I agree that some are purple).
There's blue popsicles