Why do they need so many doors like... we didn't have so many doors when we were kids.... 
Apparently they also have two sets of stairs. One article about the design says the extra doors and stairs are to speed access and egress thus enabling timetables to be maintained. There is also talk that they will have a driver and conductor, although Oyster Cards render ticket giving and fare collecting unnecessary, Boris is of the opinion that people want someone on the bus other than the driver. Dual manning, so it is suggested, will only apply between certain times and on selected routes.