Frank, you are assuming that "State Troops" were like our National Guard today. This was not the case in 1865. That was not the law. Those men who were in State Troops , Militia and Home Gurads companies were men who were otherwise exempted from military service under the conscription laws. They were men who had been in most cases discharged for illness, or injury, or age.
I know that you are looking at, well if they were soldiers they were subject to being called for duty, and in their States they were. The Conscription Law was passed in 1862 because during the reorganization of the Confederate Army from 12 month enlistments to "3 years or the War". many men able bodied opted to not reenlist. The same happened in 1861 when State Volunteers refused to join the "Confederate Army" when their regiments were converted to "National Service" and joined State troop companies.
The defence of Richmond in 1864 also included many of the Virginia State state troops militia and home guards an invalids in those trenches. But what you are asking as I am understanding it is why didn't Georgia and alabama send their home guard also? the simple answer is that those states governor felt that their home guard were as needed at home and with good reason.
Bare in mind that when we are talking about State troops and home guard we are talikng about the old and thos younger than 15 and the other those who are militarily unfit. Men with only one arm, men with not enough teeth to tear a cartridge in the normal manner, and such. These people were your firefighters and constables and such in their communities and were much admired in Dickert's account in his book "The History of Kershaw Brigade". Captain Dickert in 1865 was only 18 and the Captain of a 1st line company in the 3rd South Carolina Infantry and had served the entire war coming up throught the ranks from a private shoveling sand for fortifications for batteries at Charleston Harbor in April 1861.