In the South, it has much to do with the myth of the Lost Cause. The Confederacy, a fledgling nation building upon the spirit and foundations of their revolutionary forefathers, up against the superior numbers and strength of the North, a monolithic evil comparable to that old monarchy of England, and fighting to the last. This whole concept is what drove much of fighting after the Civil War, and with Stonewall Jackson dead, there was no better living figure to commemorate the memory of the South than Lee.

To add to his status as a survivor, Lee, unlike other Confederate generals, posed the greatest-but not the only-threat to upsetting the Union and turning the war in their favor. Lee, along with his subordinates, forced the North to react to every movement they made until Grant took charge and dethroned and defamed Lee by using his same tactics. Likewise, Sherman tearing a hole in the Confederate heartland around Terminus, Ga and through Columbia, SC weakened the image of Lee to the North.

Source:The Confederacy as a Revolutionary Experience, This Terrible War