One of the best things about our U.S. Constitution is the separation of powers. Many will contend all this does is cause gridlock that prevents progress from being made, yet the founding fathers would say this is good.
Very few countries have a bicameral legislature and a separate executive. Most have an executive branch that is of the same party as the legislature, and there is rarely any gridlock. Laws that are written rarely have a problem getting passed.
That's not the case in the U.S. It's very difficult for a law to be passed by both houses, and then by the executive branch. The founders wanted this because they wanted to make sure minorities have protection. They wanted to make sure legislatures couldn't pass laws that were to the disadvantage of minorities.
If at the last minute someone thinks a law is a bad idea, it's not too hard to throw a wrench into it in the U.S. In other countries -- in most countries -- it's hard to stop bad laws from getting passed.
The founders made it this way because they wanted to make sure no bad laws got passed. They wanted to make sure laws made were good and benefited the masses as opposed to one group of people.