Other contributors have said "How big are some guys balls?" is the same question as "Why do some men have big balls?" If you believe that these are not asking the same thing and should be answered differently, click here

Why do some men have big balls?

Answer:
Genetics.

Much like other body parts they can vary greatly from person to person. As others mentioned it is all about genetics. Though there are some aliments that can cause shrinking or extra growth.
All of them don't. They vary just like penis size.
First answer by Abjelde. Last edit by Moygo. Contributor trust: 30 [recommend contributor recommended]. Question popularity: 5 [recommend question].