The Answer for this is quite simple some soldiers do and some do not there is a lot that goes into body building and bigger is necessarily always better. Secondly Soldiers would have to be eating a massive amount of food to maintain such a body type which is not always available and then there is the nature of genetics in this blog you can see pictures of dwaynes and vin disel father and it can give you a better in sight in to why they are the way they are.
Genetics play a huge role in how you look and soldiers quite frankly often times are not provided enough caloric intake to support such a large structure. For other examples of just how genetics can affect your height take a look at north korea the average height there is 5.5 for men and 5.1 for women, or look at south korea the average weight there is 151 pounds for men and 123 for women while in america the average weight for men is 197.9 pounds and a height of 5 feet 9 inches and for women the average weight is 170 pounds and 5 feet 3 inches. So this is the reason not all soldiers will look like the most buff body builder as genetics, caloric intake and general life style choices make a big impact on just how large muscularly an individual can get. The united states military tries to feed there soldiers for performance and performance does not mean very large as in a battlefield the bigger you are, the bigger the target as such the u.s military is not keen on having very large soldiers as a matter of fact the army in particular has a height and weight test which is typically administered every 6 months failing this is grounds for separation regardless of if its all muscle you have a maximum weight for each height