Most designers suck at design.

Consider the convergence of design of laptops and smartphones. If designers were competent, we would see a multitude of designs, since a good design must be designed for something, analoguous to how optimization must optimize for something. Given the extreme similarity between available designs, there are presumably a significant number of professional designers incapable of generating anything interesting. (I would wager most laptop/smartphone designs at the moment are designed as cheap apple copies, which makes for no differentiation since everything else is designed for the same.)