Because the whole system is quite resilient and self-repairing, and probably requires a great deal of consistency between the various genes? Aging is quite fundamental to life, and a "bug" in that area would almost certainly cause severe problems in other areas, probably death. Cancer might be an example. And systems of many components tend to narrow the standard deviation of the composite.

But that's just guessing. The article might not even have found something profound, but a life-style effect. On the one hand, we're living long (historically speaking), on the other hand, we have unnatural habits.