Having worked to help engineers design better, I think it would be more accurate to say "non-designers build ugly products." It's just that the engineers are building products, and in the process, they're designing them. Since they're usually not trained as designers, they don't turn out looking so nice sometimes.

Engineers are every bit as capable – if not more capable – as learning design as any other person who wasn't "born with it" (which I haven't seen to be a requirement). But, since most of their energy is going towards one type of thinking, it diverts cognitive resources from doing another type of thinking.

Engineering requires logical thinking, whereas design requires that you be able to let your brain go quiet and let your unconscious take over for a little bit. From what I've seen, once engineers have seen a logical way of understanding what makes a good design, they have a framework on which to bind logical thinking to their experiences with design, and iteratively progress.

(P.S. I think this article could just as easily be called "designers make unusable products.")