Continuity mistake: When 9 meets 3 and 4, they open his zipper. During this scene, several close-ups show 9 with the zipper closed and open again without anyone closing or opening it.
Continuity mistake: When 9 created the "torch" from a light bulb, it needed to be turned to work. However, when 3 and 4 investigate the bulb one of them simply puts it in and it starts glowing without being screwed.
Continuity mistake: During the funeral scene for 2, a tunnel with steel bars is seen in the background, with none of the bars broken. When the camera angle reverses once 2 has floated into the tunnel, one of the steel bars is broken.
Continuity mistake: When the Seamstress is sewing 1, he falls and the coin falls off his hat. However, in the full shot, 1's coin is back on his hat.
Continuity mistake: Little metal washers are seen on the table behind 9 when he comes to life. There is a wide shot later, and they are gone.
Continuity mistake: 9's zipper does itself up after 2 has inserted the voice box in him.
Continuity mistake: After 9's unleashed the Talisman on the killer robot, 7 runs over to congratulate him. 7 puts her hand on 9's shoulder, but then in the close-up of 9, it's gone.
Answer: They were sent out into the world to create a new world for themselves. Every time the scientist created a doll, he transferred part of his soul into the doll bringing it to life but leaving him weaker. After creating 9 and transferring the piece of his soul into 9, he died so they would never have found out what they were created for.