Why people are unable to blink their eyes if dry?

Lack of lubrication. Your tears act like the oil in the engine. They lubricate the surface of the eye with t= a combination of water, oil and protein. The proper balance of these three componant is necessary for the proper lubrication. When the eye is dry, the lubrication does not occur and the eyelid surface sticks to the eyeball surface. The blink becomes painful by scratching the corneal surface.