Why does each state have two senators?

In the Constitutional Convention, small states worried they would be outvoted by bigger states. The Senate was designed so every state gets the same voice there, no matter its population. This was part of the Great Compromise that balanced power between large and small states.

At the Constitutional Convention, large states wanted representation based on population, while small states wanted equal power. The Great (Connecticut) Compromise created a two-part Congress and gave every state two senators so all states have equal representation in the Senate.