For the same reason that a defendant may not be presented to the jury in handcuffs or in a prison uniform. Because we humans are not able to return to a blank

For the same reason that a defendant may not be presented to the jury in handcuffs or in a prison uniform. Because we humans are not able to return to a blank slate, free from biases imparted by information later learned to be false. For methods that are known to be useless, the jury shouldn't be asked to perform the impossible.