Maybe they didn't, but if they did it was a sound economic decision.
It seems that Transocean over-insured the Deepwater Horizon by a whopping quarter of a billion dollars. The insurance companies have paid off, $401 million to date with more to come, without even a cursory investigation. Transocean is making a sweet profit from the disaster.
Torching your own assets for the insurance is a time honored, if frequently illegal, business practice. Of course, very little is illegal for oil companies.
Given the results where BP and the federal government bears all of the costs of the blowout while Transocean reaps nothing but profits, one could say that Transocean would have been fiscally irresponsible had they not destroyed their own rig. Of course, it was probably just a lucky accident.