Jason Wilson: It's us.
Adelaide Wilson: They look exactly like us. They think like us. They know where we are. We need to move and keep moving. They won't stop until they kill us... or we kill them.
Gabe Wilson: Who are you people?
Red: We're Americans.
Gabe Wilson: If you wanna get crazy, we can get crazy.
Red: But the soul remains one.
Answer: The project was abandoned, but they obviously kept the tethered ones alive. This may have been out of some sense of compassion, or because there was a possibility they would be useful in the future.