All art is a combination of objective and subjective aspects.
The objective improvements from css here include: shorter lines are easier to read (per multiple legibility studies), the styling distinguishes navigation and secondary site elements from the main content (without css you get a half screen of navigation links), and the visual importance of in-page anchor links is reduced.
It is way more readable with CSS, I don't know what you're all on about.
The font is bigger, the lines are shorter, the navigation doesn't take half the page. The only thing worse would be the contrast but it's not that bad.
I don't know about most people but to me seeing bits of my desktop on the sides of the window I care about feels like visual noise. I like to have all my apps maximized but maybe is that just me ?
How having bit of your desktop showing on the sides any different than whatever background image or color a particular website decides to show on each side of the text?
I prefer having a quiet single color background and being able to dictate how wide is the text I am reading than being limited by the website owner's choice. But that is also maybe just me.