Why were Washington, Lincoln, FDR considered great presidents?

Answer 1

Because each served during a time of change and crisis and rose to the occasion. The successors to two of them, Adams and Truman were considered very, very good because of the more complex issues afterward, while Lincoln's successors Johnson and Grant were considered failures and corrupt with consequences we still feel. Note also that the presidents during WWI are not considered great and their failure probably helped lead to WWII.