There are many possible ways to answer this. I would suggest that you check in your text or your notes to see if there is one specific answer that you are required to come up with.
I would argue that the differences in these two systems reflect the fact that American political culture is generally more suspicious of the government than European political cultures are. The United States began its existence with a rebellion against heavy-handed government and the political culture of the country reflects that beginning. Americans do not trust their government and therefore do not want to put too much power in the hands of any one person or political party. For this reason, they set up a system in which the executive and the legislative are separate from one another and can check one another.
The American presidential system, then, reflects the fact that Americans trust their governments much less than Europeans traditionally have.