Based on what I've read, while the TOP KILL method has worked in the past, there were no guarantees; this method has never been tried in water this deep. Surely the top, top, engineers and scientists knew about it, but they knew about other, less risky methods that might have had a better chance of success.
It's easy to look back and criticize them for doing things that did not work. It only seems like they are doing very little because you aren't reading about what they have been doing. With all the pressure on BP, on Halliburton, on the operators and owners of the rig, and all the pressure on the Government to get this thing capped, you have to believe that they are working around the clock.
Remember, you are dealing with a well head that is a mile deep, and almost three miles below the seabed - you can't just scuba-dive down there and shut off a valve.