"My God, my God, why have you abandoned me?" Jesus shouts from the cross. It's a genuine cry of anguish. His father abandoned him because he cannot look on sin. Why then did he plan for his own Son to become the embodiment of sin and have to be treated this way? For this reason: to save his elect people from their sins.
Mark may have been inclined to exclude a detail which could cause difficulties, but the Holy Spirit saw to its inclusion. It's awkward theologically because it hints at a fracture within the godhead. Instead, we propose the human nature of Jesus refused the comfort of his divine natuire, and it's in that state he expresses his tormented loneliness.
We see too how, even in the midst of this darkness of sky and of soul, Jesus still has trust in God and knows he shall be delivered when the punishment is over.