You're operating with a limited field of view and range of movement on a very small and often deep area. Microsurgical procedures in neurosurgery are usually long so fatigue becomes a factor. Often the procedure may affect blood flow to the brain, so you need to move quickly. All of this can affect surgical skill. Although robotics represents the wave of the future, humans will never be replaced.
Robots are tools to augment our skills.
It will always be important to have a skilled surgeon leading the surgery.