Exactly, there's a stereotype of Engineers being white men with a Gillette shave and a perfectly clean hard-hat, which is, in and of itself, a lie, but because of that, people generally expect Engineers to be male, white and in their 20-30's.
Because companies realise that this is what the consumer expects, they go out of their way to produce the image the customer expects to see, including using the same image in their own advertising, which serves to strengthen the belief and close the circle.
Edit: It has to be mentioned though, as I think someone mentioned earlier, that the problem is on both sides of the fence, people do builds walls around what they believe they are capable of, but it's a lot easier for corporations to break those walls than individuals.