Answer:
Because of fear.
Step-by-step explanation:
The context for the early US was that they had just fought a revolutionary war against a tyrannical, powerful government, and so when forming their own government, the founding fathers along with most, if not all, early Americans decided it would be best to maintain independence instead of risking another tyrannical government taking over. Due to this independence, an extremely weak government was formed under the Articles of Confederation, which made the US a "firm league of friendship" and disallowed the government any ability to regulate or coordinate the states in any capacity, leading to chaos in currencies, a lack of taxation or funding for maintenance of the nation, disorganization of trade, and so on. As a result, the founding fathers came back together to form the Constitution, which would clearly set out a strong foundation for a truly United States, with a federal and state government system.