Obviously, because they thought they had never been true Scripture. The Early Fathers were fallible men and the Reformers believed they erroneously included the books.
1600 Years of Use and 7 Books taken out by men forming a bunch of NEW Churches.. but leaders didn’t make the Change it was 2nd Generation, Leaders didn’t stop Rosary Praying...either next Generation chucked it out! A Reformation of the Reformation..haha