Is right that some time after the treasures were discovered most of them were safe in museums and the supposed big companies, but what about the rest? Common people could still find them and transform at their will with no restrictions, some of these people use them for the good, use their transformation abilities to help others and the city. But sadly that was not everyone's case, many people used them to unleash their chaos through all the world and make true their distorted desires with the power of transformations. And as they could turn invisible their treasures they could hide their identities.
That's why some people with treasures worked together do defeat this kind of evil people, some of them liked to work alone, some villains have stolen these called "TF heroes" and enhanced their powers, there's a vast amount of stories related to this subject.