Moving walkways can be designed to move, twice as many people as a people mover. And they can easily put two or three running parallel, which can be very helpful for DLR crowd patterns. On a busy day have all running to the parks from 7am to 10 am, then one going each way midday, and all going to the parking from 9pm to 12pm. When they need maintenance you can't shut one down and run the others. When they break the people can simply walk rather than need to be evacuated.
They follow the KISS principle.