Why did Parker keep his reserve out of the close action?

Why did Parker not send a few ships from his reserve to reinforce Nelson?

They probably could not arrive in time, and Parker still needed the reserve to cover against possible enemy reinforcements.

A viewer asks why Parker did not send a few reserve ships to reinforce Nelson. They probably could not have reached the close action in time to change it, and Parker retained them against the possibility that allied or other enemy reinforcements might approach the battlefield. The decision illustrates how a commander must preserve security against an uncertain wider threat even while a visible subordinate force is under pressure.