Because the way the technology works is the way it works. The way you want it to work is a backwards design.
Do you mean you want to read white text on a black background, and have white screen refreshes?
let's be serious. Just deal with the way the technology works.
It's just like with LDC tvs, the black point isn't black because the backlight lamp is always on illuminating the rest of the image. The pixels are only set to black and some light still shines through. It's a limitation of the technology. If you have a serious issue, you have 2 choices.
1) don't use the technology
2) become an engineer and improve it