It's quite simple, if more waste goes in, more waste comes out. It's one of the first noticeable improvements for new raw fed dogs. Not only is the amount much less, it's drier and easier to pick up.
If you left this waste over a few days it would biodegrade back into the earth as raw does not contain synthetics and fillers like processed kibble does. This allows for the body to easily absorb the greatest amount of natural nutrients without a load of unnatural ingredients left over. Meaty bones and bird proteins can account for the poop turning white, this is completely normal. Dark tarry stools are also normal when first switching to raw as well when switching proteins.