Ultimately, all organisms reproduce, whether sexually or parthenogenetically, to replicate and pass on their genes to future generations of their population.
So that way the human race can continue to grow and expand. It's also a way for our descendants to remember where they come from.
So our species doesn't die out
Some of us do, some of us don´t.
The need to reproduce is imbedded within the human genome, because without reproduction, we would eventually all die out.
As you can see in the chart, the total human population is steadily increasing overtime, which is a sign that we won't all die out and that people are reproducing. (Though, there might be a point in time where the population is too much to habit the entire globe).
Now, some people choose to not reproduce, and they don't do it throughout their lives. So, one can't say that every human NEEDS to reproduce, because it isn't a requirement. It's just recommended for a variety of reasons, which all depend on the person.