It would potentially mitigate the risk identified by the GGP regarding “unreliable” contractors who force risks on you that you may not want. Same reason I often choose to do house maintenance myself. Not to say it’s also not without costs/risks, it just comes down to which balance you prefer.
NASA still makes these competitive contracts though and picks among several contractors. Afterwards NASA is still involved in design through reviews and other lines of communication.
Using your analogy, if I do hire a contractor I'll talk with them a lot about what they're going to do and make sure it's generally in line with what I want, but they're generating most of the ideas and just incorporating what I say.
Eh, not so much. They have reviews, but it is a much more hands off approach. *
There were instances where NASA engineers brought up issues with designs and were told it wasn’t their role to drive the design. The concept of CCP was they were buying a ride, not a rocket. Just like you don’t tell Airbus what engine they should use when you buy a plane ticket.
* IMO the goal of CCP was to find a mechanism to informally circumvent many requirements. NASA could always waive requirements but I don’t think many people were willing to sign on the dotted line even if they disagreed with the requirements. CCP unburdens them from the same requirements while also allowing them to avoid full responsibility for the decision. (More charitably, it also allowed them to avoid some political costs, like having to spread projects across multiple political areas to avoid funding cuts.)
Right, reviews, where important design concerns can be raised. IDK what specific design concerns you're referring to, but just because an issue is raised doesn't mean it's a real issue.
Again, you don't want two different organizations trying to design one thing.
Not really. Early rockets included multiple private contractors like Douglas, Boeing and NAA, but those were basically government projects top to bottom.
Single vendor commercial rockets are a recent (2000s) invention.
Think of how wasteful and inefficient multi-vendor rockets are as a concept. What complex machine would you engineer in such a way? Would you have the government, rather than buy cars from Ford, GM, Tesla, etc, instead contract out the production to one company for the motor, one for the frame, and one for the interior and instrumentation?
It was the only way to do it at the time, no company would have had the capacity for such a project, including reserves for damages. And even in private businesses it is common to outsource specific elements to external suppliers. The Saturn program was massive.