Question

Why are most maps unable to depict the earth accurately?

Answer 1

The biggest problem why most maps can not depict the Earth accurately is the shape of the Earth. The Earth is rounded, elliptical shaped body, and the most of the maps are made as cylindrical or cone shaped, and in that manner it is just impossible to depict the Earth as it naturally is.

Also, the practicality of the maps is very important, which is why most maps come as rectangular, because they are the easiest and most practical for using. If they come in few pieces, or with multiple different shapes merged into one, they would not be practical for usage.

So despite the distortions that appear on the maps, they are still preferred because of their practicality, as the ones that can depict the Earth objectively have shapes that are not practical at all.  

Answer 2

The Earth is a spherical shape and maps are flat 2-D shapes,so this makes it difficult to size the exact proportions correctly because they just don't mix. It's like trying to make a flat mask for your face.