3 Nephi 6:18

Now they did not sin ignorantly, for they knew the will of God concerning them, for it had been taught unto them; therefore they did wilfully rebel against God.

They did not sin because they didn’t know better. They knew what God wanted from them because they had been taught. So they chose to go against God.

They weren’t sinning out of ignorance—they knew God’s will. It had been taught to them. They were rebelling on purpose.