Why?

Because this has been going on for years. It did not just start a few months ago and quickly get revealed. That means this happened under their own governments, for years, the ones they served in and headed.

This investigation of some sort is absolutely necessary (I dont know or care which type, but an investigation is necessary). I can only imagine the committee discovering past Ministers of Internal Security, those responsible for the police, and maybe others as well, being discovered as either having been asleep at the job or being complicit. I can only imagine the irony of them calling for the investigation thinking they are harming this current government only to discover they will have brought themselves down int he process.