Final answer:
Administrative agencies' rule-making has caused an increase in the executive branch's delegated powers.
Step-by-step explanation:
The increase in the executive branch's delegated powers has been caused by Administrative agencies' rule-making. Administrative agencies have been granted the authority to make rules and regulations by Congress, which effectively delegates some of its legislative power to the executive branch. This allows the executive branch to have more control and decision-making power in areas that were traditionally within the purview of Congress.