Fat stores can provide feedback regarding hormonal regulation. The stress hormone, cortisol, is linked to the accumulation of belly fat. If you're looking to lose abdominal fat, identification of all life stressors is an important piece of your weight management puzzle. Your exercise program should be modified according to your stress burden. Although this study is done with women, the same applies to men.
Additionally, lower abdominal weakness (abdominals below the belly button) is very common among both male and female trainees due to society postural dysfunctions like anterior pelvic tilt (forward shifted pelvis) which essentially inhibits (or turns off) the lower abdominal (LA). If you have a weak or inhibited lower abdominal, you can have the appearance of a pooch belly. Crunches will not strengthen the lower abdominal as the LA is controlled by a different set of nerves (ilioinguinal and iliohypogastric). Correcting anterior pelvic tilt involves more than strengthening the LA so get a professional to help you as there are many things to consider. This video may help you.