With long life comes the merit of maturity. The brain never stops learning. The way the neural circuits are updated is very sustainable and open-ended. So it pays to aspire to live on.
Gautama Buddha came to "great enlightenment" at the age of 35. History tells that there was a prolonged aftermath of the momentous event. He went on to live until the age of 80.
Coming to an intimate understanding of the mystery of the universe, the ultimate cause of the suffering of humans and all living things, seems to be so final that it feels strange to go on living after the climax. Even if Buddha's life after the enlightenment was an anticlimax, there should have been many poignant points through the course, as he went on to breathe and communicate and expose himself to the imperfect occurrences on the earth.
It is not difficult to imagine there must have been ups and downs. Earthly events seems to be strange to follow the great enlightenment. The truth lies in that strangeness.
The greatest blessing of long life might actually be in that sweet strangeness of the gradual ailment and deterioration and alienation from the earthly joys of living.