A lot of people don’t realize that Washington had a tarnished reputation in 1776. There had been a well-known incident during the French and Indian War when troops under Washington’s command had supposedly killed some French prisoners after they had surrendered. Washington was never officially charged (he was, after all, on the winning side) but there were accusations that he had violated the laws of war.
Perhaps as a result, Washington became a stickler for following the rules during the American Revolution. He wanted to not only follow the rules but also for there to be no questions about his actions.