The first reason is the states get to chose the Senators. “All U.S. senators have been chosen by direct popular election.” A popular vote is really just a form of selecting a candidate or taking up an issue based on most of the total voters in an election. The Senate is part of the government that makes laws and The States choose the people to make the laws.
The second reason is The States are represented in Congress and have rights to make their laws. “Each state sends two Senators to represent their state in the U.S. Senate.” Two of the Senators (which The States chose) are sent