How about downranking sites that do not redirect back to their desktop variants when a mobile URL is shared and then consumed by a desktop user? Mobile sites can be consumed on desktop browsers, but the experience is not always as good.
I find it odd that the redirect is typically only unidirectional.
Yes you're right that this is also a problem. Along with mobile versions of sites that offer no link to the desktop and vice-versa. Some smartphone users might not want the mobile version for whatever reason.
Luckily there's browsers such as Firefox for Android that allow add-ons. One of the add-ons I have is called Phony which tricks the website into thinking you're on a desktop browser. Often the browser's built-in "request desktop" option is not good enough because the website uses modernizer or something like that to determine if you're mobile.
I find it odd that the redirect is typically only unidirectional.