First, there exists a plethora of Jewish perspectives, so I'll simple offer my view.
Torah - which I view as an evolved, remarkable human effort - is many things, including brief, issue oriented pericope, splotches of etiology, more extensive folk history, and superb meta-narrative. I doubt that either the story teller or his audience were at all concerned with how well the Cain/Able tale flowed from that which came before. This concern, and the creative rationals engendered by it, were left to those later generations who chose to take these tales as literal, holy biographical writ.
In a nomadic culture wherein such things as family, clan, chesed, and hospitality were items of paramount importance, it was valuable enough oral tradition to effectively paint this tail of the First Crime, insist that God holds us to be our brothers' keeper, and note that His justice was not to be tainted by those (presumably future offspring of Adam and Eve - Sarna) who might feel free to extract blood vengeance. Later, these lessons/principles would serve well as efforts were unfolding to congeal and sustain a brit-centered tribal confederation soon to be known as Israel.