Willful Ignorance and Clearing the Underbrush

According to 9th Circuit Judge Alex Kozinski, willful ignorance amounts to knowledge of criminal activity. This was reported earlier today.

Judge Kozinski is a well-regarded jurist. See
here, here, and here..

This jury instruction is known as a "Jewell instruction" in the Ninth Circuit.

One of dissenting judges,
Judge Susan Graber, said that this kind of instruction creates a crime that does not exist in the text of the statute, and that this instruction "transform[s] knowledge into mens rea more closely akin to negligence or recklessness."

So, if this is a serious problem, why has the "Jewell instruction" existed in the Ninth Circuit Model Jury Instructions? Why has it not been changed since 1976?