It’s not that native speakers ignore grammar, it’s that they do it on instinct. Being a native speaker of a language is a very different thing to having learned a language from a book. Only through a large amount of exposure can you build up that instinct.
Native speakers spend most of their time in their native language. They think in it, they chat in it, they bear their soul in it. They know the nuances of a language. They will often know that something is phrased incorrectly, but not know why. They will be able to pick up on nuances, and in some cases even be thrown off by a perceived nuance that someone gave that they didn’t intend.
Grammar books list rules and explain how the language works. Native speakers know the rules instinctively and know how their language works. Prescriptivists (those who prescribe how a language should work) and grammar books (especially bad ones) have little impact on native speakers.
The worst, and I have experienced this, is people who try to tell you that what you said is wrong. I know that there are some nuances that are lost on second language speakers, or that nuance doesn’t exist in their native language.
The sentence was “I love language”. They told me that it should be “I love languages”. They said it was because if I just used “language”, I had to specify which language. But in this case, it was referring to the concept of language as a whole, not one specific language.