Aerial firefighting aircraft do not put out fires. They support suppression/containment lines to an extent. They're very expensive to operate, and, except for trials continuing in Victoria - do not operate at night, where they would be more valuable.
It would be cost-prohibitive to purchase large tanker aircraft. And the time between dump, return, refill and return is significant. They would be unutilised. These aircraft rotate around the world during northern and southern summers to fight global fire campaigns.
In some instances - aircraft are sent only to pacify community against actual fire suppression value. The best methods are the rapal guys that jump out of helicopters and do controlled burning. They're highly effective.