They’re evolutionarily hardwired to do so for the best chance of survival in their habitat. Their brain isn’t as complex as humans so it doesn’t need as much time to mature.

Their bodies are also more mature, so they are able to do the things they need to do right away.

All living things have instinct that they are born with. Even supposedly "helpless" creatures like human babies. Yes, you need to do a lot to take care of a newborn baby, but a newborn is born with certain instincts that allow it to survive. For instance, if you put a nipple (or a bottle) in a newborn's mouth, it will instinctively suck on it. If newborns didn't have that instinct, they wouldn't be able to eat.

I've seen 3 months old babies that fall in water and start to swim to the surface and then turn on their back and float. That is instinct to me...

If anything, behavior that is based so much on learning is the unusual outlier. In the animal kingdom, primates (and mammals in general) are strange for how much they have to learn. Its far more efficient to have neural circuits already designed for the skills you will need. The tradeoff is that we are incredibly adaptable to the environment and culture that we live in and can continue to add skills and nuance to our repertoire for many decades. I may not have been born knowing how to navigate the Sargasso Sea, but at least I could learn how to post comments on Reddit.

It's evolutionary. Turtles who moved to the sea were less likely to be eaten by birds. And the the faster they raced to the sea, the better the chance to survive and pass along their genes. Multiply that over millions of generations and an instinct is created. Ultimately that's what all instincts are, baby creatures born with the instinct that benefits their survival were more likely to pass on their genes and make more babies. It takes a long damn time to do, but evolution is slow.

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