I know calories in < calories out = weight loss, but some people also just have different body shapes. A teammate is a fast Cat 3, in his late 40s, rode 13,000 miles last year and still has a paunchy looking stomach. Sometimes genetics win.
For the majority of people you're talking about, yeah. They just eat too much after rides. I don't think calorie counting apps that dramatically overestimate your burn do people much good either. Oh, your 16 mile ride where you didn't exceed 130 bpm burned 900 calories? Ok.