Why wasn't Goering's morphine withdrawal depicted?

That indeed would have been interesting. Apparently, after getting weaned off morphine, he lost about 30 lbs. and regained a lot of his mental faculties. Speer remarked in his memoirs that they could have used this renewed mental acuity to end the war a lot earlier, before it became such a monumental defeat for Germany. They were losing anyway. Hitler, however, did not care about this.

The withdrawal was long before the trial, so would been a distraction to stretch the timeline of the story back a full year.