There is an important distinction between a manufacturing defect and a design defect.
With a design defect, it can be argued that the company intentionally made the product a specific way, and the way they chose was dangerous. This may not have been intentional on its own, but they should have seen the danger and taken steps to find a better design, rather than negligently pushing forward.
With a manufacturing defect, the design itself was fine. The company tried to make a safe product. A mistake was simply made while the product was being produced, compromising it and making it dangerous.
On the whole, though manufacturing defects are a valid reason for a case, they don't show up as often as liability cases involving design issues.
Part of the reason for this is the scope of the case. A company may make 100,000 units. A manufacturing defect might impact 10 or 20 units. They "slipped through the cracks" and endangered a few individuals.
A design defect, on the other hand, impacts all 100,000 units. They are all potentially dangerous and many people are put in harm's way. This is why you'll sometimes see mass lawsuits where numerous consumers ban together to seek compensation for design defects, especially if the company tried to cover them up, but this is less common with manufacturing defects.
Again, both may be valid reasons for a lawsuit, and it's important to know your rights after an injury. It's also good to know the differences between the two and how that can impact your next move.
Source: FindLaw, "Defects in Manufacturing," accessed June 23, 2017