Given that the rocket blew up more or less at launch, it should be full of unspent fuel. How does one put out that fire? I'm guessing there's a lot of energy stored there, so letting it burn through doesn't seem wise.
I think the only thing to do at that point is contain wildfires ignited by the burning propellant. The other commenter's entirely right: it's not practical to stop a combustion reaction where the fuel and oxidizer are already mixed.
Here's a ground-level view from a similar solid-rocket failure, for some perspective:
That stuff is fuel and oxidizer mixed together. It is nearly impossible to stop once it gets started.