> What if the robot fails?

Touche. At least you can send another robot!

But in reality, the ideal system is probably a combination of built-in redundancy / spares for parts that can work that way; and then robots for the kinds of things that are too complicated to have a built-in failover.

The robot fails to perform the task or fails reaching orbit,etc?

Send up another [improved] robot. These missions are less costly than human missions. We get to iterate more often

> Send up another [improved] robot. These missions are less costly than human missions.

Says who? And how? This seems like an unsubstantiated claim.

Robots don't need air, food, or sanitary facilities.

Launching to space is severely constrained by the mass you can bring up. You can send up multiple robots compared to the mass needed for all the food, life support ect, for a single person.

Instead robots need fuel & more infrastructure support to move around and retrieve tools & supplies.

So again, [citation needed]. We don't have, and are no where close to, general purpose miniature lightweight robots, after all.