Targum Pseudo-Jonathan on (Genesis 4:25) slows the Torah down. Adam did not immediately father another son after the murder. The Targumist tells us it took a hundred and thirty years.
"Adam knew his wife again, at the end of a hundred and thirty years after Habel had been slain; and she bare a son, and called his name Sheth; for she said, The Lord hath given me another son instead of Habel whom Kain slew."
Midrashic tradition (Bereshit Rabbah 20:11) holds that Adam and Eve lived apart during these 130 years, mourning Abel, mourning also that their other son Cain had become an exile. They refused to bring another child into a world capable of producing Cain. But at the end of that long grief, they came back together. Seth was the child of reconciliation.
Eve's words carry the whole story in one sentence. "The Lord hath given me another son instead of Habel whom Kain slew." She names the grief directly. Seth is not a replacement who erases Abel. He is a repair that acknowledges the wound.