When nothing stays put on its own
On Earth, gravity does a huge amount of invisible work for any manipulation task. It holds objects on tables, keeps tools from drifting away when set down, and gives a robotic arm a stable, anchored base to push against. In microgravity, none of that is available. An object released mid-air simply stays where it was released, or drifts slowly in whatever direction it was last nudged, and a tool that isn't secured can float off entirely. This changes manipulation from a task of moving an object against a mostly stationary background into a task of managing momentum and contact forces for every single object involved, including the robot itself.
The more subtle and important consequence is that manipulation becomes a two-body problem. When a robotic arm on Earth pushes an object, the robot's own mass, anchored to the ground or a heavy base, absorbs the reaction force without noticeably moving. In free-floating space operations, the arm and the spacecraft or platform it's attached to share momentum with whatever is being manipulated. Push on a satellite to align it for capture, and the reaction force pushes back on the servicing spacecraft too, potentially altering its position, orientation, or spin. Every motion has to be planned with this coupling in mind, because a manipulator that ignores it can send both itself and its target tumbling in unintended directions.