In Vietnam, many people do not have cars, so they use bicycles to transport cargoes (such as simply the shopping or merchandise to sell) by placing them in the middle .. between the handlebars and the saddle. Carry them on a scooter would be much more complicated, because it's faster and harder to control. Another reason is that the brakes perhaps are broken, and sit back allows them to put down their feet more easily to stop the bike. Finally some people, like in the photo work by bicycle through the streets of the city picking up and collecting plastic bottles or cans or even paper, that can be recycled.
They use two bags in front of the bicycle to fill with whatever they find. Then sell the "booty" for pennies to the recycling agencies. Driving in this way allows her to get off the bike and brake faster, might otherwise leave the bottle behind and turn to go back with all that load is rather difficult (also someone else could take it before her).
Therefore often you see people driving these Harley Davinson also without any cargo to carry, because they are simply used like this.