Why there is no recoverable data in my android device?

This happens only in two cases; firstly, if the files have been deleted for a long time as they may be overwritten by other data. Secondly, in case the files were delete recently and you have done any new operation on the device like adding new files or installing new application on your Android device. In both the cases, deleted or lost data cannot be recovered as they are overwritten with new file content.