Congress did not want to join World War II for several reasons.
1) No country had attacked the US personally for the first couple years of the war. The US doesn't join World War II until after the attack on Pearl Harbor on December 7, 1941. Before that, no US citizens had been hurt or killed because of World War II.
2) Economic reasons- The US was still working on getting out of the Great Depression of the 1930's. There was still a high unemployment rate and hundreds of thousands of American citizens still struggling financially. This made foreign affairs less of a priority.
3) Trade- The US's ability to trade with foreign countries was almost completely unfazed by the war. The US was still able to make deals with the countries it did before the war started.
All these pieces of information show that Congress really had no stake in joining an international war where thousands of American soldiers could die for a cause that many American citizens didn't believe in.