While McKinsey has a global staffing model, allowing for manufacturing opportunities across various offices, the firm's Midwest offices, particularly Chicago, have historically had a strong focus on manufacturing clients.
This makes sense, given the Midwest is home to over ~50% of the US's industrial manufacturing base. McKinsey's Chicago office, serving as the NA Operations hub, has likely played a significant role in supporting these clients.
That being said, it's essential to remember that McKinsey's manufacturing expertise is not limited to specific offices. As a global firm, they can deploy experts from various locations to support clients worldwide.
So, while Chicago might have a stronger manufacturing focus, it's not the only office with expertise in this area.