Why?

This condition known as Motion Agnosia, which is extremely rare. One with Motion Agnosia can struggle in performing the activities of daily living.
As,
▪️ Pouring a cup of water because the fluid appeared to be still and they do not know when to stop, also the movement of the fluid rising will not be perceived.
▪️ Trouble following conversations because lip movements and changing facial expressions were missed.
▪️ Crossing the street and driving cars will be their great difficulty because moving vehicles appeared jump rather than moving. The cars can be far away, then suddenly appeared right in front of them.

It typically results from damage on specific area of the occipital or parietal lobes in the brain that may cause from,
• strokes
• dementia
• brain cancer
• states of anoxia (loss of oxygen supply to the brain)
• developmental disorders or other neurological conditions.

Agnosia usually affects only a single information pathway in the brain. For motion agnosia patient, their other cognitive abilities like thinking, speaking and interaction will still be functional so they will train to use their hearing sensory to estimate distance for their living.

Like Motion Agnosia, many more visual agnosia to be known, for example:
• Dyslexia – reading disability
• Colour agnosia – colour recognition disorder
• Prosopagnosia – facial recognition disability