Setting aside Georgia, which obviously sends the most undergrads to the University of Georgia, in 1998 the top ranked state was South Carolina. By 2014 it had slipped six spots. Tennessee slipped four spots. See the list below.
Rank by Year
Look how Texas has moved up, Alabama down. California (not listed above) went from 16th to 9th in 2014.
When I have time I'll map it out, but if I did you'd see the greatest percentage change lies in Texas (235.9 percent increase), from 78 students to 262 students. Setting aside small places that send relatively few students (meaning a drop of 2 to 1 comes out huge in percentages, but small in real numbers), the biggest drop is South Carolina (-63.7 percent, or 209 students fewer in 2014 than in 1998).
One hypothesis is that UGA has gotten so difficult to get into, at least compared to nearby major universities, that it's attracting smart kids from elsewhere (North Carolina, Texas, etc.). Another hypothesis, I suppose, is that universities in Alabama and nearby states have improved and have drawn more of their own students back into the fold. I'd lean toward the former, not the latter, especially if you look at the academic comparisons of UGA to, say, Bama or South Carolina.A final hypothesis may be that UNC and Texas-Austin have become so very competitive that good, but not quite good enough, students are coming to UGA as opposed to a second tier school in their own state. That's a reasonable hypothesis as well, one I have no way of testing.