Jesus died to save sinners. This is most certainly true, but there is more. All of creation is cursed as a result of sin. The evidence of this curse is thorns and thistles. The soldiers were doing more than mocking the creator. The crown of thorns points us to the truth that Jesus took on not only the curse of sinners but of all creation (Galatians 3:13).
OT Reading: Genesis 3: 14-19
NT Reading: Matthew 27: 27-31