Naomi decided to return because she heard that the LORD had visited his people and given them food. That report led her to set out from Moab toward Judah. This reason is given in Ruth 1:6.
In Ruth 1:6–7, Naomi decides to leave Moab and head back toward Judah, and her two daughters-in-law set out with her. The immediate reason given is news Naomi hears: Yahweh has acted on behalf of his people by providing food again. These verses pivot the story from loss in Moab (famine-driven migration and the deaths of Naomi’s husband and sons in Ruth 1:1–5) to movement back toward Bethlehem and the coming conversation about whether Ruth and Orpah should continue with Naomi.
Ruth 1:6–7 presents a decisive turn in the story: Naomi moves from staying in Moab to traveling back toward Judah. The text is explicit that she acts after hearing a report from Moab that Yahweh “visited” his people by giving them bread—in other words, food conditions in Judah have improved. The passage also stresses that Naomi does not begin alone.
A careful answer keeps the immediate passage, the book's argument, and the whole-Bible storyline together, so the question is answered in context instead of as a detached idea.
Start with Ruth 1:6, then read the surrounding section so the answer stays connected to the passage's flow.
6Then she arose with her daughters-in-law, that she might return from the country of Moab: for she had heard in the country of Moab how that Yahweh had visited his people in giving them bread.