Weight and portability
Let's take a look at some numbers, shall we?
Approximate weight of a six-pack of 12oz canned beer: 5lbs
Approximate weight of a six-pack of 12oz bottled beer: 7.5lbs
The difference seems almost negligible in the store, but just wait 'til you're two miles into your hike with a six-pack of longnecks in your backpack, or lugging a case of bottles to your friend's BBQ. Ten extra pounds of bottles makes a huge difference.
Add in the fragile nature of the glass bottle versus the sturdiness of aluminum cans and it almost makes planning picnic beverages a no-brainer. On the retail side, concert venues and sporting arenas love that they can dispense full beers without dangerous shards of broken glass injuring customers. And any bar or bottle shop manager will tell you they love how much easier cans are to stack and store, and how much less of an issue breakage is.