A lot of people misunderstand the role of government advisors. They do not exist to advise the government on the correct policy. They exist to generate plausible justification for decisions that have already been made. Like every other public sector job, it is about arse-covering.
First the decision is taken behind closed doors, then the advisors are asked to carefully collect some raw data and misrepresent it in a way that supports the decision.
Occasionally the advisors fail to understand this themselves and produce reports that are completely contrary to the decision that has already been taken - at which point the government simply ignores them or finds other advisors.