That's because it's generally hard to build enough volume in the abs for them to show, given that fat tends to store in the belly, covering them. As such it's often said that you get abs in the kitchen rather than in the gym, but that's about a low calorie diet.

What the post above talks about is about taking enough calories and protein for you to be able to build muscle, normal diets very rarely include enough to build muscle optimally and it can be harder to actually eat enough than to lift enough.