Question

Why did the founders of the Constitution create a separation of powers?

Answer 1

The founders of the constitution created the separation of powers so that, the writing of the constitution was not abused and the legislative, executive, and judicial branch have a say if they feel it is being abused. 

Answer 2

they made that document to avoid abusive power, so if the constitution got too big, the separation of powers could intervene and prevent it from doing any harm