At the scale of billions, likely yes. But right now, we don't have working practical self replicating robots, but we do have humans. The cost of the 15+ years

At the scale of billions, likely yes. But right now, we don't have working practical self replicating robots, but we do have humans. The cost of the 15+ years is externalized, you can just lure a desperate already-grown human with shiny promises, give them some training, and ship them off. Yes, you have to ship them oxygen and food, which is expensive, but it's a solution that exists and works with todays technology (minus some well-defined engineering), while the robots aren't ready yet.