Raising the young would require an investment from the parents that may compromise the survival of both. By abandoning the young, the parents increase the odds of their own survival, which allows them to have more offspring later.
Work Step by Step
Spreading resources between the parents and offspring can, in times of scarcity, lead to the death of all. If the parents allow their offspring (or some of their offspring) to die to preserve resources for a smaller group, their odds of survival increase. The parents and any surviving offspring can then continue their lineage.