My reading of Tech secession was officially, the "140 rule" the total number of football and basketball players one could have on scholarship. SEC schools (schools, not teams) would "overrecruit" and "cut" football players late in the summer, too late to find a spot on a team at another school. Dodd despised that, feeling that outside of egregious behaviour by a player (and sadly, we see far too much of that today), you recruit 'em, you keep 'em on scholly for the four years.
The above is pretty much the official line of Tech's SEC departure, as our official ACC departure was pushing for lower academic standards (shame on us).
Tech was competing well enough in the SEC. Though not officially stated, I would not be surprised if the
Darwin Holt hit on Chick Graning played a role in the departure, although likely not the straw that broke it. Dodd also talked about wanting to play a more national schedule.
But my point is that if you consider your league to be regional, you don't expand the footprint.