This is a great question produced by close reading.
The answer is that it is an intentional riddle, with the answer that Leah, as a type of the prostitute-bride of the church, was already dead when Jacob, as a type of Christ, died.
For those unfamiliar with the deep riddles of scripture:
Consider the mechanism by which the invisible God, who cannot be seen nor heard, reveals himself.
The fish swim where they will, and the stream nudges them where it wills. God says that Israel will become a parable משל.
The people of the Bible are like the fish, swimming where they wish, unable to see the water. God is like the water, nudging the whole of history to accomplish his purpose.
He causes a language to be formed which has meaning to it's very 'yods and vavs'; the dots and strokes which make up the Hebrew square text. (Notarikon) He causes a blossoming author to observe the fish, yet remaining a fish himself. The author records what he observes using the language God has given him to write two manuscripts simultaneously.
The first concerns the actions of the fish. Unbeknownst to him, the words he freely chooses have been nudged by the stream to write the second manuscript within the words of the author. This manuscript speaks of Christ. This is the nature of Paul's "Mystery, hidden from the beginning."
The author remains ignorant of the second manuscript because the metaphor concerning Christ is not known until after the cross. Only hints of the second manuscript are available.
Prior to the cross they could see that Adam came from the ground (adamah) and is made of blood (dam) and spirit (the aleph). But they could not see that the blood דם was the commandment ד finished by the son ם.
They could see that light sounded like skin (puns). And that God had given a garment like light to cover his sins. But they could not understand that God himself would cover our sin by his holiness, until after the cross.
Because of the mechanism and effort to write the second layer of scripture, there is nothing superfluous. God did not tell us that "he gave the grass for the cattle to eat" because he thought we didn't know that cattle (sheep are cattle) eat grass. Grass forms the seed used for bread. Jesus is the seed. He was beaten and baked (tribulation), into the bread. (by way of symbols). So he was laid in a feeding trough, with grass, surrounded by cattle as a promise of the cross... the baby bread.
This is context for the answer to the OP.
In the genealogies of Cain and Seth, the word 'lived' is used for the ten generations of Seth, and not used once in the seven generations of Cain. These genealogies are the basis for solving the riddle of Rev 17: Of the seven generations of Cain (all shadows of Christ), five were (they did not live), one is (Enoch on both genealogies walked with God), and one is to come (Lamech mean's power and Christ will come in power). The full solution is elsewhere.
The riddle of Leah is similar. As the symbol of the bride before the cross, she is already dead at the time the Christ-type dies.
Eph 2:1 ¶ And you [hath he quickened], who were dead in trespasses and sins;
All the proofs making her the type of the prostitute-bride, and Rachel the type of the virgin-bride, are subjects for other questions.