Here's why:

* Vast diversity: Insects are incredibly diverse, with an estimated 90% of all animal species being insects.

* Abundance: Insects are found in nearly every terrestrial and aquatic environment on Earth.

* Evolutionary success: Their small size, quick reproduction, and adaptability have allowed them to thrive in a wide range of habitats.

While there are still many undiscovered insect species, the sheer number already known makes it the most populous taxon on Earth.