Like any company, BP looks at the opportunity cost of making decisions.
Unfortunately, they lack the necessary prowess for making good business decisions. Instead, they took a risk by cutting corners (such as safety, and buying inferior equipment, etc) instead of putting money into the cost of materials (such as BNSF, who spends MILLIONS of dollars ensuring their rail network is maintained regularly).
For BP, the opportunity cost of fighting "potential" legal issues outweighed the significant up-front cost of drilling with superior equipment safely!
So the way I see is when it came funding the plan, they see it as a potential legal (and long-term PR) "cost-saver". I think they wanted to reduce the legal exposure as much as they can, and 20 billion dollars is probably a helluva lot cheaper than fighting THAT MANY MORE COURT CASES down the road!
Long story short, it's all about cost to those incompetent buffoons.
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