Lots of site owners disable zoom because they think they know best when it comes to content-size. Disabling zoom also makes the site slightly more responsive because when a touch occurs, the browser doesn't have to wait a few hundred milliseconds to see if a 2nd finger is going to be touched to start a zoom action.

Yep, as of iOS 10 https://webkit.org/blog/7367/new-interaction-behaviors-in-io...

And thank god for that, there were so many sites that disabled zoom for seemingly no reason, and somehow it was always the ones with tiny text or images.