Someone above said Dorian didn't train abs, he did, HIT crunches, 2 sets, to failure. He talks about it in his book Blood and Guts (out of print).
People who don't train abs don't understand the importance of anterior chain strength.
Good point. The anterior chain exerts exponential force to the weight lifted to keep everything in place, it's not just the posterior side doing the work.
I a bet a lack of ab training contributes to the lack of gut control in modern bodybuilding. If you're not regularly training them and maintaining that mind-muscle connection, it's much harder to have on-demand / constant control.