They're always shitty porn mentioned in a /v/, /co/ or /tg/ thread that they can't post there (worksafe!) so they post them in /r/.
We have a /b/, an /h/, and a /d/ last I checked.
Another problem is that you can't really tell if this was actually requested, short of going to the board they mention and searching through all the recent topics. It'd be quite easy to just say "Posting this for /tg/" and go and spam whatever the hell you want in /r/.