Then they led him out to crucify him.
(Mark 15:20)
If Jesus was already dead under the tortures of the Roman soldiers (=euhemerized archons of this age), then he couldn't (logically) carry the cross. Hence the need of Simon of Cyrene.
Curiously, the Ascension of Isaiah has only the corpse of Jesus crucified:
And the prince of this world will lay his hand on the Son of God, and he will kill him, and he will hang him on the tree, and will kill him, not knowing who he is.
(Ascension of Isaiah, 9:14)
The question is: cui prodest?
The Romans crucify living victims, not corpses. But then who obliged the Cyrenaic were really Romans? The emphasis on the foreign provenance of Simon could serve to distinguish him from the indistinct mass of Jews, i.e. the Jews obliged a not-Jew to carry the cross, since Jesus was already dead.