You don't get to change the deliverables of cost plus contracts without re-negotiation either. That's not the risk that is being avoided here, the risk is that the company is going to decide to ask for more money for the same service they initially promised.
For example with Boeing's recent starliner tests, they would be asking for more money to fly the orbital flight test that they initially promised, because they fucked it up the first time.
For example with Boeing's recent starliner tests, they would be asking for more money to fly the orbital flight test that they initially promised, because they fucked it up the first time.