We are not born tabula rasa. Did you ever see a calf get born? It knows how to get onto its feet in minutes, find its mother and start feeding. That's hard-wired. Hormone secretion? Hard-wired. Reflexes? Hard-wired. Creating memories? Hard wired. Identification of sound direction? Hard-wired. Face recognition? Probably hard-wired too. Our CNS comes with a ton of instincts and basic processes. Why wouldn't that extend to other areas?

In contrast, the world is too complicated to learn through exposure. Something has to structure our learning process. Language is (in principle) not learnable, only when you make enough assumptions. Those assumptions must be coded somewhere in your brain and probably genes.

Tabula rasa sounds nice, but it is untenable and utterly lacks evidence.