Most normal people would ask this question, but this is Apple. It is highly doubtful that the person that gave you the antenna requirements knows why either. You would probably get the following "make it a stainless steel strip on the order of x dimensions and a structural part of the phone". Again, that is a guess, but I doubt anyone as low level as an engineer would have known that it would be an exposed design element. I read that employees want to know as little as possible. That way, if there is a leak, they can rightfully claim ignorance. I guess when it gets right down to it, as an engineer, I'm just hopeful that a fellow engineer wouldn't be so naive to think there wouldn't be problems with this. That is why I don't believe this problem is engineering driven from the bottom, thus more engineers or different "talented" engineers is the answer. It is obviously driven from the top either a process problem (keeping design teams separate) or a cultural problem (ignoring sound engineering advice).