If you try to go left-to-right, you will quickly realize that at the end of each "line" it is really difficult to know where the next line starts. It is easy to accidentally start again on the same line (and inspect the same elements), or skip one accidentally. Then navigating through the elements one by one requires a considerable amount of cognitive effort, your eyes bounce up and down constantly, and you end up inspecting the same elements multiple times.
If you try to go top-to-bottom, lane by lane, you will then realize that the page also has infinite scroll and you will never go past the first lane.