It comes from a period of time when logical empirical thought were things. But the truth is, we're actually a bit of both. We have genetic knowledge (for example a baby knows how to cry without first having to learn it from experience). And we have things we learn.

Plato was the guy who pushed innatism hard. His argument was that all of the ideas are just out there floating (THE FORMS) and when we learn we're not learning new things but remembering things that already exist.