If there is such a thing as reincarnation, then why is the world population still growing?

In Sikhi, when looking at populations, we aren’t looking at human population but population of souls.
Can anyone say with certainty that the population of souls is increasing?

If we look at just this earth, the number of plant species and animal species are decreasing. Perhaps they are being reborn as humans. Not just that, Sikhs don’t consider just this Earth to be part of God’s creation we are told by Guru Nanak Sahib Ji of countless planets and even universes. Who is to say that those lives aren’t being reborn here?

The answer to this question is not knowable by anyone but Waheguru but it’s hardly a difficult question to resolve according to Sikhi.