Answer:
The executive branch has so many checks because this is the branch that could become the most powerful if such checks did not exist.
Step-by-step explanation:
Because the executive branch concentrates military and spending power, the president could easily become a dictator if the executive branch powers were not as limited as they are.
The founding father wanted precisely to keep the president from becoming a dictator. They also believed that Congress, not the president, should be the most important government power.