I hate to nitpick, but this is not entirely true.

First, there is no innate, specific grammar or syntax in the human brain. Any given language -- even one's first language -- is learned. It's learned in stages, and true, one tends to pick up the rules by immersion before studying them consciously. But conscious study of the rules is extremely beneficial to improving one's understanding of, and facility with, a given language.

To say that "no conscious understanding of the rules is required" is a little like saying "Kobe Bryant is a naturally born basketball genius." True, Kobe Bryant may have certain athletic gifts and mental wiring that enable him to exceed 99.999999% of the world at basketball skill. But he learned the rules of the game, just like everyone else. And he practices daily. In fact, he probably practices harder than many of his less talented peers. Even someone of his natural endowments couldn't have risen to his level without conscious and repeated effort.

It's true that grammar and syntax start to seem natural and subconscious over time, especially as one improves in linguistic fluency. That's a good sign, in fact. But I've never met a writer who couldn't benefit from conscious study of the rules and fundamentals, even if only occasionally.