And he does. He marries Ruth after he has cleverly dispatched another more closely related kinsperson (my, Naomi seems to have kin pouring from her earlobes!) from having Ruth (4:1-6). Ruth quickly becomes pregnant and bears a son. And at story's end, all the men disappear. The women of the neighborhood turn to Naomi and say, "Blessed be YHWH, who has not left you today without go'el. His name will be proclaimed in Israel! He shall be for you a returner of life, a nourisher in your old age. Surely, your daughter-in-law who loves you has borne him, she who is better for you than seven sons" (4:14-15)! And that, as I have said, is a patriarchal mouthful!
The redoubtable Ruth, ever risky, ever devoted to Naomi, is heroine here. It is she who has moved the empty, famine-haunted world where the story began to a rich, fecund community, full of joy and hope for the future. Only once in the entire story is the word "love" used, only as a description of Ruth's love for Naomi. It is that love that has molded and driven the tale; it is that devoted love that molds and drives the universe of God.