The Deepwater Horizon well didn't just up and blow out one day. That well had been a beast for months, and everybody knew it. That is why the crew that experienced casualties was there to P&A (plug and abandon) a well they knew was too dangerous.
I've long speculated that the drilling crew experienced a "loss of circulation"...or catastrophic loss of the drilling fluids that normally contain a release of gas from a productive formation. On any drilling rig, such an event is a religious moment. If it happens concurrent with being in...or immediately thereafter finding...a gas-producing formation, you are about to have a wild well. This is when your BOP (blow out preventer) comes into play. But, by the time you can activate it, things may have already gotten very interesting. You can have a miles-long string of drill stem starting to displace out of the hole, and through the derrick crown, and there is just no good place to be when that happens. You can also have a blasting geyser of natural gas, or poison gas, blowing out of the well, searching for air and ignition.
Well, we learn more details from a Bloomberg piece (h/t Hot Air) that seem to support that there were, perhaps, multiple circulation loss events on the Deepwater Horizon, and that would explain why they were in a P&A operation. It was just a bad, bad well.
In the drilling industry, you have those; you just make them safe, and go on (which is what the crew was doing when the well blew). You have holes you drill that produce nothing. You have holes where you experience formations that collapse or shift to bind your drill stem. It's more difficult to drill for oil than most people begin to understand.
There are lots of interesting loops the Earth throws, and motivated, very hard-working people meet them to provide us oil, and the standard of living we enjoy.