Why Hair Volume and Shine are Mutually Exclusive

You've all seen close up images of human hair (usually taken with a scanning electron microscope).  If you recall, hair is made of layers of scales of keratin, much like a stack of paper cups.  If those scales lie flat, the hair is smooth and reflects light, thus looking shiny.

 If the scales separate from each other, the hair will look less shiny but will have more volume as the scales between individual hairs will push each other away.
Since we rarely want flat or dull hair, we need to make some compromises between volume and shine.  
Shine products, however, are great! They can allow some of the scales to separate and fill in leaving the hairs somewhat thicker but also smooth and shiny.