If two states disagree, what alternative would you suggest? “Flip a coin and move on” or “Just give in to the other side” are solutions that are likely to be abused: one rogue state can wreck havoc by making unreasonable demands. Going to war over it seems worse than spending millions in court. The courts ARE our inexpensive, fair way of resolving disputes (even if they aren’t as inexpensive as we might like).