Cite needed.
Classic depicted the empire at peace and at the height of its power. While I wouldn't use "stale" to describe the state of the game in the mid 80s, there is a limit to the product line in such a setting. Looking at other RPG settings, you see one of two things: Static (or driven entirely by player actions) or rapidly destructive timelines full of war. Because war is interesting. Traveller adopted a calendar approach as soon as the setting launched, so big events were inevitable.
Each edition's choice of era and location allows a different set of plots and stories to be told easily. The moving calendar allowed some of that, but GDW found that their quarterly JTAS schedule meant the Fifth Frontier War was over in two issues before the calendar marches on. To tell the stories of a long, wide spread, and interminable war, a bigger event was needed. (MT)
To tell tales of recovery after a civilization shaking event, you need the civilization shaking event. (MT to TNE)
To rebuild an empire (T4), you first need to destroy one.
A new discovery that brings a long quiet era to an end requires the long quiet era. (T4 and T5)
Exploration needs frontiers and civilization's edges (T4, T20, and TNE)