Because computers are supposed to be practical first. We're still making significant enough improvements in the performance of them that they outweigh things such as aesthetics. The things you mentioned have negligible improvements year after year and the way they differentiate between each other is the looks.

This is also why good computers are affordable by almost everybody, but things like good bicycles, furniture, watches, coffee machines etc are not.

You can buy a decent computer for the same money as one chair.