Why does each state in the USA have to legislate for same marriages isn't there one universal ruling?

Every state does have its own rules. There is no universal rule because the federal government does not decide the requirements for marriage; the individual states do. They also have individual rules as to everything from the minimum age to drive a car to the statute of limitations on credit card debt. Other than things that are controlled by the federal government, there are universal rules in the U.S. for almost nothing.