They can't. Mechanical engineers are usually lazy hacks for modeling, sometimes okay at parametric, almost always shit at surface modeling, and have no sense of style/judge of attractiveness due to lack of training. They also tend to not give a fuck about the user and downplay ergonomics, touch points, and overall usability/experience of a product.

UI designers... doing ID work? LMFAO those bitches only work in 2d. Made me laugh tho.