Breaking down complexity into its component parts, a common theme in American thinking, is also at play in American decision making. Individual decisions are always a part of larger decisions. They can be either grouped or isolated. Because Americans value focus and execution, they tend towards isolating decisions.
The more clearly defined the decision to be made, the more limited its scope, the greater the chances that it will be made intelligently and implemented effectively. Limited scope decisions are also a form of risk management. Their results can be evaluated quickly. They allow for flexibility and rapid reaction to changing parameters.
And if human action influences the very context in which one is operating, there is a point beyond which grouping decisions increases risk. From the American perspective systems are inherently risky. For if just a few key elements of a system are wrong, the entire system is wrong.