Why doesn't linear resistance scale proportionally with the square of length?
You are confusing several basic concepts.  The E field of two point charges in a 3 dimensional space follows a \$ \frac{1}{r^2}\$ relationship.  If instead to two point charges, you use two infinitely long wires running parallel to each other the field is proportional to \$\frac{1}{r}\$.  So the dimensionality really matters. In a resistor there is one path, if you double the length of the path it will take twice as long. The electric field is confined to the interior of the resistor.