Starting out with the baseline design, a typical men's underwear brief without any specially constructed pouch will tend to compress your package in a way that the majority of what would make up the look of a bulge will fall between your legs.
Although not uncomfortable, this tends to leave a minimal profile to your underwear package. For the longest time this was essentially the only style of men's underwear. More often than not, this "flat-front" design makes a guy seem slightly diminished for all but the most endowed individuals.