It would do well with a tiny amount of additional CSS to make it work well on large screens, but I guess they don't want to make it too nice to use for that segment.
IIRC, this site was put together, in particular, for low-bandwidth users (like mobile phone users back in the feature phone day) where every byte cost. CSS would be an unnecessary and potentially expensive addition for those users.
It's not optimized to that level. There's 1.1k of inline tracking javascript. And a reference to an external stylesheet for the styling, along with a bunch of wastefully long hex identifiers.
Took a look at the dev console, there are 2 tracking scripts, segment and CNN specific one. Those take up the majority of bandwidth. There's also a separate CSS style sheet. The main DOM and the stylesheet are <10% of the total bytes transferred. The favicon is the same byte size as the entire DOM.
Don't think there is necessarily a consideration of byte cost, given the size of the tracking scripts. A few lines to make this manageable on wide monitors aren't prohibitive for those users.
The website already serves a 496 byte CSS file (359 minified, even less gzipped), addition of a max-width to make it readable on large screens wouldn't make a difference.