That is an important principle of Westminster government. The elected representatives do not carry out investigations, and manage the details of those kinds of things, because they are elected. The separation of their role from the independent and non-partisan public service is important in ensuring independence and fairness. All of those principles are necessary in terms of ensuring fair outcomes, and procedural fairness for individuals through processes, such as investigations.
On March 26th, 2021. See this statement in context.