Why do animals with fewer offspring look after there offspring for longer?

Your question is unique, and I like it. This is not completely true, for a mother alligator can have more than a dozen babies and unlike other reptiles, will watch over and protect them until they are ready to be on their own. Bears are good example of being protective mothers. The average number of cubs a mother bear( A.K.A. sow) will give birth to is two. The best answer I can give you is that animal mothers who have fewer offspring need to be more careful because they need their children to grow and to continue to reproduce(the life cycle). When more babies are born in one litter, there is more hope for that species to gain more production.