They're linking to the mobile version because they're entering the comment with a mobile phone that makes it far easier to copy the full URL and makes it, well,

They're linking to the mobile version because they're entering the comment with a mobile phone that makes it far easier to copy the full URL and makes it, well, not difficult, but harder than with a full keyboard to edit out the subdomain. If I'm on a desktop, have a moment, and see one that's particularly egregious, I often respond with a comment to the full version linking to the appropriate table of contents anchor.