Why did Benigni divide the film so sharply into two halves?

Since the film is primarily a comedy, the first half does not deal so heavily with the Holocaust, thereby allowing the film's more lighthearted and magical moments to take center stage. The viewer remembers this portion of the film throughout the second half and is thus reminded that, even though the stakes have been raised, the characters generally are normal, happy people who have been forced into a difficult situation.