[checoivan]

Even if they use ingredients from a single store it'll look 1000 times better in the picture.

The photog gets to choose the best bun out of hundreds, the best tomatoes, greenest lettuce. In the end photograph, the bun will look perfect and fluffy, the tomato sparkles, and the meat seems fresher than a live cow. Plus they may or may not, but there are "tricks" to simulate things like fake steam coming out of food, spraying glicerin or corn syrup to make it look moist(looks like water droplets), or simply cold food photographs better. On top of all that, good lighting does wonders as well.