You're picking at the difference between the proximate cause and the ultimate cause of the ad looking the way it does.

    Q: Why does the ad burger patty appear thicker and larger?
    A: Because we made it *this* way [show process].

Sounds reasonable to me. Perhaps you wanted an answer more like,

    A: Because we wanted to show off all the ingredients in the
       best possible light, to encourage you to buy it.

It actually takes a few why/because cycles (i.e. root cause analysis) to approach the ultimate cause; for example:

    A: Because we made it *this* way.
    Q: Why?
    A: Because it makes the burger look good and it shows
       you what's in it.
    Q: Why?
    A: Because if the burger looks good and you know what's
       in it, you'd be more likely to buy it.
    Q: ???
    A: Profit!!!

Alas, the original question did not stipulate a particular kind of answer; I think the response, as given, sufficiently answers the question.