What if........,
We read that Cain and Abel both brought their sacrifices to the Lord, now I think we can all agree they weren't babies, but either teenagers or young men that knew their occupations from experience, so with that in mind,
Eve bare a son and named him Cain, meaning I've got a man, could she be thinking, hoping he was the one that would crush the head of the serpent? Now remember after experiencing the perfection of the Garden she had lived under the curse for at least nine months, certainly she was hoping Cain was the one and life would go back to what it was like in the Garden, however as time passed it became evident to her he was not the expected/promised One, then she gave birth to Abel and was so disappointed in him she named him emptiness, vanity, unsatisfactory, then 130 years passed, which logic and human nature suggests she and Adam made more babies and then it's recorded Seth was born, but by this time, after living under the curse for 130 years she didn't hold much hope in Seth being the promised one, becasue he was named, let's just watch this one, consider he ways, what will he do?
The point being, Eve had lost hope (women, can you imagine 129 child births) so the reason Seth was even named in the Story is God's way of showing us, giving to us the name of one man (as there are many others named throughout Scripture) in the genealogy of his Son proving/authenticating He was the son of Adam, the fulfillment of the promise given to His great grandfather that He would crush the serpents head, ...hence His title, the Last Adam........, and is not to be considered a chronological record of the children born to Adam and Eve, ...but it is a parenthesis in the account of the life of Adam.
Blessings,
Gene