Very simply, I see the RCMP as the subject matter expert. The RCMP, more than anybody else, is going to be aware of whether an investigation or a review has the potential to interfere with an ongoing criminal investigation.
Frankly, I think such a restriction is perfectly justified, because I think it's important to remember that the review of any civilian review or complaints body can take place after the investigation has been completed. So it's not necessary to step in at an early stage and risk causing difficulties for an investigation.