[cflsystems]

I think the logic behind it is if you enter box dimensions it means the product ships on its own.
The UPS module will pack all products in cart and calculate in multiple boxes based on weight and box dimensions from the module's settings. I guess it is assumed if you want to enter box dimensions on product level that product ships in its own box with its own shipping cost.
If you add box dimensions for all products but they still ship together in one box what's the purpose of the dimensions? The cart will still ignore them as what matters in this case is total weight and default box dimensions and the service.
I could be wrong but it seems irrelevant to me to have box dimensions on product level unless you intend to ship the product separately from the others in cart.