Robots are expensive, software is not. I can instantly duplicate software 1 million times and run it in parallel, I can't just produce 1 million robots. Physical world is always harder.

Even if we get robots who can, say, build roads start to end, there is still a HUGE gap between that and it actually being used. There is a hard floor, too. Robots are made of physical things, physical things have scarcity, and there's no way around that to our knowledge. Even if you can build the robot for 1 cent, the material cost will still exist.