It's the way the whole construction industry has gone (and indeed others, as per your Boeing example).
When I started working for a civil engineering contractor in the 1970s, everything we did was inspected and approved by Resident Engineers and Clerks of Works, representing the client, designer, or both (often the same organisation in those days).
Since then, clients have largely dispensed with in-house engineering expertise, having outsourced the design as well as construction. They've been unwilling to pay designers to carry out an inspection role, and indeed few of the engineers in design consultancies have the necessary construction experience to do that effectively.
So the whole responsibility rests with the contractor's QA system, and the ability and honesty of the staff applying it. I have to say that the colleagues I worked with until retirement were (almost!) without exception rigorous in applying it correctly, but there is always a temptation not to do so.
We also had to produce and deliver to the client, comprehensive Operation and Maintenance Manuals (O&Ms), detailing everything from design inputs and records, through construction and as-built drawings, to equipment specifications, maintenance schedules and methods, H&S information, and even guidance for eventual decommissioning and demolition. These were very time consuming and expensive to produce, sometimes after a contract had made a loss as well, so again there can be a temptation to cut corners. That shouldn't ever happen, but it's human nature.
Unfortunately, when these corners have been cut, something like Carmont can suddenly expose them many years later, with possibly disastrous consequences.