because it probably wont work. the depth they drilled to in the earth under the ocean is pushing it out at 100,000 lbs per square inch. We do not have the engineering to seal this leak. If they get it sealed like this is will be a miracle.
The BOP (Blow Out Preventer) would have stopped it - if it had worked in this case.
It worked on other occasions @ similar depths though, "just" not this one.