The value of a geezer who was 300, 400 or 500 years old was always greater than a person who was just 100 years old or less!
If the former was a mech designer or scientist, then he must have mastered an immense amount of advanced knowledge. Each year they lived, they could produce all kinds of amazingly useful contributions to society, from researching new applications of hyper materials to increasing the effectiveness of many applications of phasewater technology by 5 percent!
The productivity of these old fellows who had managed to earn a lot of merits to prolong their lives by several centuries was insane. They were living treasures of red humanity and an important part of the core foundation of their race.
From a purely utilitarian perspective, it made a lot of sense to kill a bunch of disobedient expert pilots and ace pilots to prolong their lives!