Why was the creation cursed if it was not responsible for Adam's sin?
Creation was cursed because God subjected it to vanity, not because it participated in Adam's sin. The context says creation 'didn't have anything to do with Adam's sin,' but was subjected 'by reason of him who hath subjected the same in hope,' pointing to God's promised restoration and redemption.
Les teaches that the creation was made subject to vanity, which is the curse, and it was not subjected willingly. Creation had nothing to do with Adam's sin; it was subjected by reason of the one who subjected it, and that subjection was 'in hope.' As soon as Adam sinned and the curse fell, God immediately promised a time of restoration. So all creation is constantly looking for the day when the curse will finally be lifted. Les connects this to the seven terrible years in Revelation and to Jesus' words about travail in Matthew 24, explaining that the travail is connected with delivery--the delivery of the planet from the curse. From the day it was subjected, God promised a coming day of redemption for creation.