industrial engineers aren't real engineers. neither are computer engineers, if we're keeping score
just because aspects of the scientific method can be applied to an area of study doesn't make it a science. If every person was a quantifiable source of variance, you could bias-check and control for deviance. But the reason that 'the best design' changes every couple years is based on anecdotal information more than science. Google is making shitloads of money? Let's design our offices like Google. It's usually after the fact that people attribute quantifiable gains to the industrial design.
Don't get me wrong, things like LEAN engineering, SPC, and other process engineering is definitely science. But what color of purple to paint the walls is not, or what lighting fixture creates the ideal work environment is not. A lot of industrial engineering is glorified Feng Shui, but they'll never admit it.