Beer was in the front of our store, until they quit blocking off the aisles on Sundays.
Actually, that originally had to do with refrigeration. The refrigeration units are unsightly, so they are at the back of the store. Milk is stocked from the back, unlike non-refrigerated goods that are stocked from the front. The entire room behind the milk is refrigerated. This also helps keep the temperature more constant.
Another reason is that refrigerated goods were added at later times. Everyone had a cow, then the milk man delivered. It wasn't until the last half of the 1900's that milk and beer were added to stores.