My hypothesis is that, when a complaint is filed with the police, it's usually established that the material is indeed child pornography. The police then look to obtain the necessary warrants to take action, which requires time. The web host is then asked to remove the images. The web host will claim that it didn't know, that its system is complicated and that it will remove the images as soon as it can technically do so. Soon after, another police force in Canada makes the same request.
There doesn't appear to be any concerted action. Since the requests come from various police forces, they don't see the full extent of the issue concerning these companies. Each police force believes that it's doing its job. However, there's no comprehensive approach to investigations.