Why are GTO opening ranges so tight in early positions? It says open 54s 78s UTG, but then folds 68s 64s type hands. How are these not the same hands?? I can never get my head around the theory. What is the selection process? What separates 78s from 68s???

It's something I've never really cared about, but now every man and his dog has a training site, and all I keep seeing is preflop ranges and now I've got confused lol.