Error-proofing isn't more systematically applied in manufacturing for three main reasons. First, people, including process engineers, are often optimistic and pressed for time, overlooking preventive measures. Second, there's a tendency to not address issues at their root; operators are blamed while designers move on to other projects. Third, some error-proofing techniques, like poka-yokes, can add inconvenience or time to the process, leading operators to skip them, especially under tight deadlines.