Congress decided the election of 1800 primarily because:
- No candidate won the electoral vote.
The election resulted in a tie in the Electoral College between Thomas Jefferson and Aaron Burr, which led the House of Representatives to determine the outcome, as mandated by the U.S. Constitution for such cases.
The other options provided do not accurately reflect the reasons for Congress's involvement in this election. The popular vote was not the main determining factor, and sufficient citizens did vote, which is not relevant to why Congress had to decide the election.