The reason for it seems to come from the need for Islam not to be outdone by Christianity.
"Mark 10:30 New Living Translation will receive now in return a hundred times as many houses, brothers, sisters, mothers, children, and property—along with persecution. And in the world to come that person will have eternal life."
Furthermore, as Jesus had 12 disciples, Mohamed got also the swearing of allegiance to him by 12 people, and as Jesus was able to feed a multitude out of seven loaves of bread and a few fish, Mohammed was also able to feed a multitude out of a handful of dates.
