27:45-46 What reason would cause God to forsake Jesus?

Jesus on the cross was the sin-bearer for all mankind (cp Isa 53:6; 2Cor 5:21; Ga 3:13; Eph 5:2).

But God could not look upon sin even if it was borne by His only begotten Son, and at that moment in time Jesus experienced the abandonment and despair of being separated from God as punishment for sin (cp Isa 53:5-12 with Psa 22:1; Mt 26:36-44; Mk 15:33-34; 2Cor 5:21).