Why Wasn't The Warrior Saved?

 Stories about Abhimanyu's valor and nobility are well aware. Grown up with Krishna and also mentored by him, why wasn't he saved by Krishna himself? Krishna - the one who could forsee that he would lose his beloved nephew on the thirteenth day while Arjuna had to fight the Trigatas single-handedly, didn't attempt to save him but could witness the horror of his death with his daivik vision. Why so? What was his karma that led to his death so soon at the age of sixteen without ever having a glimpse of his son?

This question can be answered in two different ways with one showing that Abhimanyu was an enemy of Krishna and other showing that he was the son of the moon god.

Remember when Krishna killed Kaalyavan(with the help of Muchukunda - a forefather of Shri Rama, who burnt Kaalyavan into ashes when woken from his sleep by him)? Well, as Kaalavan's soul tried to escape from the cave, Krishna caught it and imprisoned it inside the folds of his angavastra.
Now fast forwarding to the time when Subhadra was pregnant and lived in Dwaraka while the Pandavas and Draupadi were in exile. Subhadra wanted to meet Krishna and whilst waiting in his room, her eyes fell on an angavastra which was knotted. This angavastra was nothing other than the one in which Krishna had trapped Kaalyavan's soul. Not knowing this, she lovingly opened the knot to which Kaalyavan's soul entered her unborn child.

Thus, not finding it appropriate to save him, Krishna let Abhimanyu die and attain mukti(salvation).

Controversial to the above story, this story shows Abhimanyu as an incarnation of Chandra's(Moon god's) son Varchas.

Before his incarnation as Krishna, Vishnu requested Varchas to be born on Earth to help him uphold dharma. But, Chandra was stubborn as to allow him to do so only if he was promised to be reunited with his son in sixteen heavenly days(which are sixteen earthly years).

Thus, in order to fulfil his promise to Chandra, Krishna let Abhimanyu die a warrior's death in the battlefield.