The Church agrees that if a doctrine is not backed by Scripture, it is false. That is why Sola Scriptura is false.
However, many people can twist Scripture to their own desires. Scripture is clear that this is possible. Therefore the Church requires that doctrine must ALSO be backed by Tradition.
As I am saying sola scriptura is not intended for personal interpretation for people to twist.
As I am saying WHAT tradition? Is it backed with scripture?
As I am saying Purgatory doctrine is not backed by scripture but tradition alone.