It could be the lead time and other timing as well. Getting all the artwork done from an available photo would take time, and they were pretty much done with minor leaguers in T206 before 1911. Southern leaguers would probably have been set and art done before the end of 1909.
T205s ended too early for Stengel and it appears they ended T205s before they intended. Maybe there was art done, but there isn't enough minor league selection in the set to guess.
Jackson moved around a lot, 08-10 he was with three different minor league teams as well as getting in a few games in the majors. It's possible they didn't have a picture they felt they could use until 1910. A total crazy guess was that they wanted to include him but the same sort of contract thing that Plank may have been involved with affected him as well.
As an aside, my wifes relative started with Greenville in 1909. A fact I'm pretty happy about since that means if I find a team photo Jackson won't be in it and I just might be able to afford it.
Steve B