Thinking about this, to explain further.

Windows will suggest a particular resolution based on the hardware you are running.

A widescreen monitor can have a vastly different resolution than a old CRT.

 

By 1920 x 1080 monitors are recommended.

If someone had a old 800 x 600 monitor, that'd be recommended.

 

Recommended isn't a size, and the CSS will determine layout based on resolution.  If you are getting the mobile layout, chances are you are running a lower resolution.