My guess as to why they didn't try this potential solution first is because others, such as the "dome" idea would have allowed them to siphon off oil into a tanker and then sell it. I assume that the top kill solution pretty much shuts off the well and they can't get anymore oil from it unless they were to drill another hole which would take a lot of time and $. Yes this is just speculation but it doesn't seem that far fetched that they would be hesitant to give up on the millions of $ (or however much the oil in the well minus the cost of having to drill another hole is worth) if they can sell it to the public that that they were at least trying something even if it put their $$ before actually stopping the leak.