Here's why:

* DNA carries the instructions: DNA contains the genetic code that determines all the characteristics of an organism, from eye color to susceptibility to certain diseases.

* DNA is passed down: DNA is passed from parent to offspring, ensuring the continuity of life and the transmission of traits.

* DNA is universal: While there are variations in DNA sequences between species, the basic structure and function of DNA is remarkably consistent across all living organisms.

While there are exceptions, like some viruses that use RNA as their genetic material, DNA is the primary and most common genetic material in all known forms of life.