>I never see the Reddit mobile site and never need to tell the browser to request the desktop mode.

There is a seemingly persistent bug where reddit fails to remember preferences surrounding mobile/desktop and old/redesign. Sometimes you will click a link and the page it delivers you to will be on the mobile site, sometimes it will take you to the redesign. It's been going on for at least a year. I use reddit a lot and I run into it at least every week. Sometimes it sticks and I have to relog to get my preferences back.