Crucifixion is thought to be one of the most brutal means of execution ever devised. Since Jesus was theologically bearing in His body the sins of the world, the symbolism of the awfulness of the crucifixion was fitting for why he was doing it: to take on himself everyone's sin.

He did it willingly because of His immense love for us. He died in our place so that we could be forgiven from our sins and be reconciled in relationship to Him.

The bible says that Jesus carried his cross at least for a little ways so it wasn't like he was being dragged. Assuming this was common practice for crucifiction why not just stop be killed then and there?