A five-gallon keg with twelve ounces of beer in it still occupies five gallons of space. There are a large number of retail items unrelated to brewing that are readily available to manage beverages in bottles because lots of things come in bottles. Coolers are designed to hold bottles and cans. Openers are everywhere. Holders are readily available or free.
Kegs are extremely hard to transport.
Whether it is in the car, shipping via a carrier, or just outside on the porch. Indeed, disabled persons or people with only a moderate amount of upper-body strength may not be able to transport full kegs or C02 bottles at all. Beer bottles pack up nicely into easily handled packages, whether they are six-pack carriers, boxes or the bottles themselves. Bottles are always ready to drink with no extra work. No one ever grabbed a bottle and wondered if they had the proper equipment and gasses necessary to access the beer inside.