Ultimately accountability for the returns on investment lie with the Project Sponsor and governance team. So they should be actively reviewing and approving several aspects of the project. This should not be a 'tick and flick' type of approval, but a due, considered review with consideration as to the pros and cons and downstream implications.
If you are having difficulty with your Governance teams, it is not surprising. Project Governance is not so much "misunderstood" as "not understood". People just don’t know what it is and, therefore, what senior management needs to know or do to be effective.