Sure, you could set the widths at 96/48 and have the standard build at 24. Great min maxing and I remember a mod doing that. But then you have to re-balance the industry to support the extra width it takes the AI to fill all the slots of these bigger divisions, re-balance resources for the extra IC it takes for every nation to build to 24, etc, etc.
And you have to take into the account that the ai works better with more units to play with, something that
@podcat readily admits. Part of the division shuffling is that the ai sees it doesn't have enough units to plug in holes along a front. Then it starts robbing peter to pay paul along the front and the front starts to look like spaghetti with all the the unit pathing going everywhere. Larger templates reduces the number of units the ai has to work with unless you are also going to re-balance the manpower across the board, at which point you are making a new game.
The 80 width is based upon game balance taking all of the other game parameters into account. It is close to historical, and nothing prevents you from building historical templates. They just won't perfectly fit into an 80 CW.