Some people are genetically incapable of achieving such a body regardless of how much they workout. Yes they can gain muscle and yes they can cut to look shredded but if they lack the bone structure to carry the muscle in an ascetically pleasing manner then they'll just look strange.
It also takes some people far longer to build muscle mass.
There's loads of factors at play here. The argument is retarded since you can apply it to literally anything if you want - Why don't you have a degree in physics? - Why don't you speak 8 languages? - Why don't you play an instrument to concert level?, Some people don't WANT to achieve those goals, some people CAN'T achieve those goals and others can with either lots of time or with little time.