The battery pack is not distributed throughout the car, and it is actually designed to be somewhat hot-swap capable in the Model S.

It's just that for the majority of people, battery swapping makes no sense. They can charge their vehicle over night at very very cheap prices and have enough range to serve them all day. If you insist on taking a cross-country roadtrip, rent an ICE - the infrastructure is just not there yet (or peoples minds have not accomodated - see this article).