Why don't most vim color schemes look as nice as the screenshot when I use them?

I have downloaded many vim color schemas and tried them out, but many of them don't look like the official screenshot.

For example, vim's own color schema - desert should look like this:

But in my vim, many colors won't display, for example the background.

But some color schemas work correctly.

Why is that?

In the: Edit-> Profile Preferences -> Colors, I select the "use colors from system theme"