The allegory moves to a spot even poorer than the one just examined. This reinforces the point of the lesson, which is that God is able to nourish his children regardless of where they find themselves. The repetition of the action of going to a poor spot in the vineyard and finding a flourishing tree does not only reinforce the lesson, it emphasizes it. The progression for poor ground to even poorer ground is intended to underscore the ability of Jehovah to nourish the house of Israel wherever they might be.
For Zenos and Jacob, these two events would signify the dispersal of the ten tribes. For Jacob, it would include those taken away to Babylon. However, it does not yet describe the Nephites.