Because it means that 288 ounces (the amount in a case of 24 12-ounce bottles) will fill 25 bottles. And therefore, they are able to produce 25 cases for the price of 24. Free profit.
Really, I surmise that it has something to do with taxes. I would not be surprised at all to learn that there’s some rule about container sizes, stating that bottles 0-11.9 ounces are taxed at one rate, 12-23.9 ounces at another, and 24 and up at a third.
Decent guess, but the cans are 12 oz. Same is true of Molson Canadian. 11.5 oz bottles, 12 oz. cans. I think they’re the same size in Canada also.
To make matters stranger, Carlsberg (brewed by Labatt’s) and Molson Excel (NA) are both 12 oz. bottles. The cases of these that are imported are packaged in 6 packs only.