Can you please explain why hard-drives follow a flying head approach? Why don't they just perpendicularly fix the reader above the disk, rotate the disk and the

Can you please explain why hard-drives follow a flying head approach? Why don't they just perpendicularly fix the reader above the disk, rotate the disk and then use a linear actuator to move the reader back and forth - exactly like optical drives? The read/write arm needs speed and extremely fine-tuned movement that can't be had from a mechanical actuator. See: https://www.youtube.com/watch?v=Wiy_eHdj8kg https://www.youtube.com/watch?v=Wiy_eHdj8kg