Bill, from what I can see in the letters, the main reasons men would have left was that the food was terrible, sanitation was terrible, and men were not paid for long periods of time. Many men went home sick because of the conditions. Most also wanted to stay in the State troops rather than putting themselves in jeopardy of being conscripted and sent to a unit further from home.
By the way who were the men of the 2nd Miss.(Quinn's) you referred to that went on to serve in the 7th Miss?