The well cap is spewing so much oil because they didn't call in enough tankers to store it.
On Wednesday, the cap was collecting 630,000 gallons of oil – but it could be capturing more oil if BP had decided to put more ships on the surface to hold and process the collected oil. That means the cap will have to continue venting excess oil into the Gulf until another two ships – one which can sift gas and water out of the crude and another which will shuttle oil to shore – arrive next week.
Next week. They've had 52 days to get their shit together.