Besides which, what the hell good would the cavalry do *behind* the troops? You use horses in flanking maneuvers to get behind and surround enemy troops. Of course the picture takes liberties with that as well as horses were a rarity as they require feed and water and your average plow horse won’t work in battlefield conditions.
You don't know much about the Battle of Guilford Court House, do you, Comrade Flick?
Battle Facts: Guilford Court House
Adopting a tactic utilized by Daniel Morgan at the Battle of Cowpens, Greene formed his roughly 4,500 men into three lines. The first line was held by North Carolina militia. In the second line Greene positioned militia from Virginia. Continental Regulars composed Greene’s third and most formidable line. The concept, known as a defense in depth, was for the first two lines to exhaust the enemy's advance and inflict as many casualties as possible in the hopes of delivering a decisive blow at the third line.
(snip)
The first British unit to reach the third line was the 33rd Regiment. There, the regiment engaged Continentals from Virginia and Maryland and were driven back. The 2nd Guards, however, managed to turn the 2nd Maryland's right but were stopped in a counterattack by Lt. Colonel William Washington’s Light Dragoons and the 1st Maryland. With additional British infantry finally arriving on the scene from their fight on the second line, Greene prudently disengaged and withdrew.
Guilford Courthouse was a pyrrhic victory for Cornwallis. Despite besting the American army, he had lost 25% of his men and was in no position to pursue Greene. Cornwallis decided to withdraw to his supply base at Wilmington to rest and refit. With his army still not in condition to engage Greene by the middle of April, Cornwallis decided to shift his operations to Virginia, a decision that would contribute to the independence of the United States.
BTW, that "cavalry" is actually Colonel William Washington's 1st and 3rd Continental Light Dragoons. And they were indeed placed behind Greene's third line to hide them from the British, so that they could in fact make a flanking attack at a critical moment during the battle, just like they did at Cowpens.