In the poem, "Mending Wall," why does Frost say there is something that does not love a wall?

Sometimes it's not a bad idea to look at a poem as a kind of mini-essay.  In Frost's "Mending Wall," the narrator wants to make the point that the wall between himself and his neighbor benefits no one.  This is his thesis.  He presents a variety of points to support that thesis, and he even includes a counter-argument, the position his neighbor is taking on the matter.   The narrator's first point is stated in the very first line and used again later in line 35, a kind of refrain and review.  The "something" that does not love a wall is nature.  Nature does not build walls, and when it encounters them, it seems to do its best to tear them down, with the cycles of freezing and thawing, "the frozen-ground spell under it" (line 2), which dislocates the bottom stones.  He goes on to make the point that hunters are another problem, harming walls as they give chase to their prey, so it is pointless to maintain the wall.  And he continues to make various points, arguing with his neighbor's position, which he provides for the reader, that walls are good, that "'Good fences make good neighbors'" (line 9).  There is a great deal more to this poem, of course, than a rant against a wall. The wall represents to some degree our way of not letting nature take its course, to our detriment. The "mending" ritual represents the meaninglessness of so many of our interactions with one another.  Nevertheless, whether one analyzes as an essay or a literary text, the point remains that nature is not fond of walls.