Why do so many web sites waste so much horizontal space?

I was just using the EventBrite event management web app. It has A LOT of content to show and fields to edit. For what I'm doing right now it would have been very helpful for them to use more of the real estate of the page, but they only use the middle 30%. Why do so many sites do this (especially productivity web apps)? Does responsive design dictate that content must fit on smaller screens, even at the expense of larger screens losing usable space?

Great design resource

100 Things Every Designer Needs to Know About People (Voices That Matter) Submitted December 19, 2018 at 04:21PM by humanatore https://ift.tt/2SfGj7u