Often it would be helpful to have every plant an equal distance from every other plant in the field to give each plant perfect exposure to sun and soil. Also, the rainfall would be less damaging to the soil.
That is why the spacing between rows is reduced for plants that occupy less space... a wheat field can give optimum yields with a 3 inch spacing,but the improvement over a 6 inch row spacing is negligible. With every narrowing of the row spacing we have to be more precise in spacing of plants in the rows, each row must have fewer plants per metre of row.
As an extreme we would still plant in rows, but the seeds would be spaced as far apart in the row as the row is apart from the next row.
That becomes more and more difficult as the row width decreases. So we stop narrowing the row where we see no improvement in yield.
Many crops have no harvesting benefit from rows. Again for instance wheat is cut as though it were not in rows. We build corn harvesters to harvest based on the fact we grow it in rows, but if we had it all spread out we would build machines to harvest it that way.
Trees are typically planted in rows to make it easier to move machinery between the trees, but also because it is easier to plan to maintain a defined distribution of trees, giving them all enough sunlight and soil. But when trees self propagate, we just cut swaths of them to leave the row spacings.
We can always find a way to do things not in rows, but we may not get any improvement, likely reduction in yields.