Because the politicians and the bureaucrats in MMS and other agencies have been in the oil companies pocket for fifty years. They let the oil company lobbyists write the regulations and then do not even enforce those regulations. It is the ultimate case of the "Fox Guarding the Hen House".
The relief well intersects the deepest point to allow the muds hydrostatic weight to kill the well. If you intersect at a shallow depth it would be very similar to the top kill method and the mud would just be blown out of the hole. It will take a very heavy mud injeceted deep to kill this well.
Drilling a relief well at the same time just does not make any sense, it doubles the risk and the cost. A deep water well costs over $100 million.
Even if it miss mark--well column--if the relief well taps formation at bottom of this leaking well it will
reduce some pressure from formation slowing flow from leaking well. But best case is to directly intersect
this leaking well colimn.
Why not make relief well construction mandatory in advance of any drilling operation? Well, I'm sure that's crazy talk! Only an insane government would require the BPs of the world to drill relief wells alongside their main wells, right?
Drilling a relief well is drilling. So now you doubles the cost and double the risk of problems. BP screwed this well up as MANY have been drilled safely. Mandating that two wells be drilled at the same time would be a good way to kill deepwater drilling in the coverage area!