People are weird about gasoline. They'll drive around looking for the cheapest option, to save 2 cents/gallon. Even with a huge tank, that's less than 50 cents of total savings.
So a grocery store can offer, say, 10¢ savings, and it only actually costs them like $1.50-$2.00 per customer. That's way less than other sales that are harder to advertise and don't bring in the same amount of business.
Ultimately the psychological benefit for the shopper is more than the financial cost to the store. The others societal costs don't come in to that equation.
Not sure why NA is being singled out here. Bottles are largely the same shape (with a few functional differences, see below) no matter where they come from.
The round shape is mostly a historical artifact from early designs that were hand-blown. A hexagonal (bestagons!) shape would pack better in an infinitely large container, but since most shipping crates are rectangular, there will be wasted space either way, and round is far easier and cheaper to mass-produce. Also, as a carbonated beverage, sharper corners could create stress points and exploding bottles.
Toppling over could potentially be reduced with a wider base, but fitting in the hand is a hugely important factor for any drinking container. There are larger-based bottles, but they also need more specialized packaging and storage space. By using bottles that are similar size to aluminum cans, lots of infrastructure can be dual-purpose (I'm thinking of things like can/bottle storage in your refrigerator, for example).
Double the volume of what? Glass bottles have to be thicker than other materials, so to get the same volume as a can with the same size base, it has to be taller.
If you want to do a lot more reading, here's a few sources I borrowed from:
Those ‘shoulders’ we keep mentioning remain in modern beer bottle design mainly for aesthetic reasons. Their original function was to provide a handy place for the yeast residue and dregs to collect, so that these didn’t pour out into the glass with the beer. Nowadays, most beer is filtered, so this design feature is no longer needed. Unless you’re bottling a yeast beer like a Belgian beer, of course.
