People that lift heavy and are consistent in training will get big, most people don't train long enough or hard enough to get seriously big.
I know plenty of people who train for a few month/weeks etc and then give up as they are not huge, usually they spend a crap load on supplements and powders to assist in their failed endeavour.
Some people get big despite their training and diet, while other overthink stuff, doing 564 variations of arm curls instead of loading the bar up and doing a few good sets of one of two good exercises, this is something I have only learned later in life.