I've never understood why they don't put these rest stops in-between the roads on an interstate so that you can serve both directions with one building. I've seen this all over Europe and it seems to make so much more sense.
Because that goes against everything government stands for. Why have 1 when you can have 2 for twice the cost...
In all seriousness I think it has something to do with safety and that you don't want slow/exiting vehicles in the left/passing lane