Marketing is the greatest force in the universe. Questioning it is unwise.
While I've never had a Whopper that looks as bad as the "actual burger" pictured above, there are two reasons why the actual product doesn't look like the prop burgers used in ads:
1: If a Burger King employee spent several hours making a Whopper look pretty, as they do with the ad props, they would promptly be fired.
2: Serving the prop burgers would lead to pissed off customers and/or lawsuits. The beef patty is either *extremely* rare, or raw and dyed brown, the plant bits are sprayed with oil to make it look very fresh, the mayo is actually Elmer's Glue, and there's probably cardboard and toothpicks in there to prop things up. As to why they do this shit instead of using actual products? The real burger will never look that good. Why is it important that the prop look better than reality ever could? Marketing.
Marketing can never be adequately explained or understood, but it is a thing that exists.