They respond to "why do your burgers look different in commercials?" by answering "here's the process of making a commercial burger."
That doesn't address the fact that a stylist cooked it on a panini grill for an hour looking the perfect brown, leading to a thicker-width burger which indeed makes their advertisements a lie.
It doesn't matter if they use the same ingredients or need to show their pickles and ketchup. They've created an entirely different product for the advertisement and will continue to sell a lesser product in place of it. The only honest answer to the original question is the obvious one: because their normal burgers look like crap.