Scientifically,why nearby objects are clearer for people having myopia or shortsightedness ?

Without getting into too much detail its because the eye can't focus the light as well from far distances as close distances with myopia. This can be due to the shape of the eye itself or due to muscle weakness around the eye both preventing proper focusing on the object. If you want a more specific answer look I'm happy to give it.

Because they aren't blind. If you mean why are they able to focus nearby objects clearly, that's basically the definition of short sight- someone who can focus on nearby objects but not on distant ones. Their eye has too much curvature, and their muscles cannot relax the lens enough to focus on infinity without glasses. But they can focus on nearby objects no problem - probably closer than someone with normal sight.

Daniel is only partially correct as his explanation pertains to hyperopia. Because images cannot actually reach a focal point behind the eye, ALL distances appear blurred. The eye contains a built-in focusing mechanism that is used to compensate for mild hyperopia. This causes its own set of issues.

It's about the focal point of the pupil. In a normal eye, light is focused onto the retina, but in a myopic eye, the retina is further back, meaning the focal point is in front of it, making things look blurry from a distance. In a hyperopic eye, the retina is further forward, so the focal point is behind it, making things look blurry at close range.

https://chemistryinmedicine.files.wordpress.com/20...

Much like a camera lens. Both camera optics and the human eye follow the laws of physics.