Revamping at minimum investment pushes equipment to limits never approached during initial plant design. Understanding the fundamentals of what is going on is required. Casual manning of engineering efforts. Not all engineers are the same. Some care about their work, others do not.
Engineers also have differing experience levels.
Even reputable firms will have some people you want working on projects and some you do not. As a firm gets bigger compared to the pool of people available to work there, the firm's engineers have to approach average quality. After all, when everyone works at the same place, the quality of personal they have must be average. In major markets, like Houston, if Firm A fails to get a major project, they cut back. The employees move down the road to Firm B which did get the project.