It's largely genetic.
The shorter the torso, all things being equal, the greater the chance for cobra lats.
Look at Stubbs, Kai Green, Yates, Haney, Ronnie...all had that hanging lat look. All had very short torsos.
It's rare that a long torso will build a tremendous looking back, with exceptions such as Mike Francois noted. And even then, Francois would lose to Dorian or Ronnie in a direct back comparison, as good as he was.
Our lats all originate, and insert, in the same areas. The fibers we're born with, and how they're arranged on our skeleton, make the difference. A shorter torso just bunches up those lat fibers, whereas the longer torso stretches them out. You can only build a muscle fiber up so much...it's easier to create a dramatic flare with a short torso.
Dorian was always one to comment on this, citing this as a primary reason he was able to beat Levrone, Ray, and El Sonbaty (long-torso'd individuals).