There are a lot of costs not considered there though. It's actually mor efficient to use the post-mix.
Post Mix is a much smaller volume and weight than a corney of soda, reducing shipping costs, handling issues and the number of trucks they need.
You can stack as many as 8 boxes on a standard hand truck, shortening delivery time. Each box is 5 gallons of 5 to 1. Imagine how many cornies that is.
Corney Kegs take up a lot more space than a post mix system. In the 4'x4' wall space here at work, we have 8 different flavors and 1 box of backup for each flavor stacked in the corner. We'd need a huge room to make that kind of space to have that much soda on hand in a non-concentrate format.
'less waste' is relative. Post mix is more efficient for soda. Besides, we win--- corney kegs are as cheap as they are because they've been drumped to the recycle market.