The reason Cain is not ripped is because of genetics. Could he get ripped if that was his main focus? Sure. If you took someone genetically gifted and had him live the life Cain is living, you would have a much more shredded person. How can you deny that it is genetics that makes that difference?
You're acting like you know better than anyone how much he eats. For all you know, he is 'genetically gifted' and eats like Emmanuel Yarbrough.
The genetic variance between humans is really small.
Some severely obese people will claim that their genes are the culprit, while eating crap food nonstop and barely moving all day. Some other guy who used to be fat might have changed his diet and trained specifically to address the problem, and then people who didn't know 'endomorphic Bob' will see 'mesomorphic Bob' and assume he is just 'genetically gifted.'
People act like the genetic variance between humans regarding their metabolism / hormones / glands etc. is enormous, responsible for these huge disparities between the fit crowd and the obese crowd, when the genetics are almost identical and there is instead an enormous difference in dietary patterns, activity level and lifestyle.
A large segment of the population actually believes that the genetic difference between two people will almost singlehandedly result in a similar physique / muscularity / body fat difference to what we see between the typical horse:
...and the typical walrus:
You see people with a lower body fat % than that horse, and people with a higher body fat % than that walrus. These two people don't have more difference in their genes than a horse does from a walrus. You don't see obese horses and you don't see ripped walruses. You can attribute THAT difference, between a horse's physique and that of a walrus, to genetics.
But to get that kind of difference in humans, you have to look primarily at lifestyle choices and diet. There aren't humans with fat-deposit genes equal to that of a walrus. Humans have more control over their environment and behavioral choices than any other animal, and over the course of the last 200 years we've found ways to eat more and more calories while doing less and less work.
It is human nature, unfortunately, to look for any justification or explanation that doesn't oblige one to make difficult choices or do difficult work.
There are no humans cursed with such unfortunate genes that they might as well be a walrus.
"Humans" is not like "birds," where you might get some eagles, some penguins, some pigeons, some ostriches. Humans are so similar genetically that we're all ostriches, or all eagles.