Why do modern team sites prevent you from using the full width of a page?

Beau Cameron points to David Warners' video which explains the white space. The video clearly compares all Sharepoint content to industry leading web pages and the use of smaller (phones) devices as being a majority of the site usage. Not sure if others use SP the way we do but our SP site is strictly our internal intranet site used only by our employees who all access it via computers with 1920x1080 monitors. Don't really care if it looks clutsy on a phone since that will never be our primary use scenario. So trying to explain why MS has done this doesn't help. Dynamically sizing the screen regardless of screen resolution should be the goal as opposed to shoving fixed width down everyone's throats while trying to justify it as "the future" or that is what the majority uses. Context here is very important.