They were hoping to kill more. From ABC News, with thanks to the Constantinopolitan Irredentist:
Jul. 7, 2005 – U.S. authorities tell ABC News that British police have recovered two unexploded bombs from the scene of the terror attacks in London.
In addition, British investigators say that parts of timing devices have been recovered from the blast scene that would have been used to detonate an explosive device. This could provide evidence that would help determine who was behind the attacks, sources told ABC News….