Why wasn't i born a cat?

The reason you weren't born a cat is due to the complex processes of evolution and genetics that determine species and individual traits. Each organism is the result of specific genetic combinations from its ancestors, shaped by millions of years of evolution. You are a human because your genetic lineage follows that path, while cats have their own distinct evolutionary history. Ultimately, it's a matter of chance and biological processes that define the species into which one is born.