The reason humans nurture their offsprings way longer than any other species isn't because their offsprings cannot survive until a very later age.
In fact, human offsprings have proven throughout history, and until this day in many parts of the vast world, to be capable of becoming independent and even more successful without their parents' aid at an age as young as 5 years old.
The reason many human societies and civilisations changed into nurturing their offsprings far longer, which also seems to extend the more developed we become, is purely economical and emotional.
Economical, because we wanted to increase survival rate of those offsprings until they are capable of both mating and putting in physical and mental labor into use.
Emotional, because we have become the worshippers of our offsprings since we are narcissistic worshipers of ourselves to begin with.
If we stop being too narcissistic and stop optimising the hell out of everything, you can safely say goodbey to raising kids so long. The survival rates will drop a notch or two, but they'll def. stabilize around a more environmentally harmonious levels, I bet ya!