A two party system

Why student believes We have a two party system, where people tend to only vote for Democrats and Republicans?

This comparison examines the differences between the policies and political positions of the Democratic and Republican parties on major issues such as taxes, the role of government, entitlements (Social Security, Medicare), gun control, immigration, healthcare, abortion, environmental policy and regulation. These two parties dominate America’s political landscape but differ greatly in their philosophies and ideals. Joe Biden vs. Donald Trump