No flames intended here, so keep that in mind
This policy is what keeps OCR's forums from turning into GameFAQs. Favorites threads are just spam threads; rarely does any real discussion come from them, and considering how many times a "favorite Final Fantasy/Mario/Sonic/Metroid/Castlevania/weapon/FPS/condom/nipple piercing/whatever" thread's been made in the past, it's a dead subject matter here. It really was beaten into the ground quite thoroughly. And if they're allowed in again, it'll all go back to a front page filled with "what's your favorite ______" threads.
When it comes to remixes and peoples' favorites, such threads become a ratings thread, something djp has always been against. Plus, VGMix had a tier system. The problem with it, was that unless a given remix was in the top two tiers ("Stuff of Legends" and "Awesome" if I recall), visitors simply weren't overly interested. They more often than not passed on songs that were rated as "Good", because they weren't "Stuff of Legends". And as if that weren't enough, there were good songs that got buried in the bottom tier because of a single review where the reviewer just happened to not like the song (and then no one else touched it as a result).
OCR already judges the songs that get on the site. They don't need to be further judged by the listeners, so that you wind up with songs no one listens to because a few people didn't like them. That would defeat the entire point of OCR's judging process.
As the old saying goes, you can't please everyone. But OCR's done just fine with these policies in place, and I can't imagine djp's going to reverse them anytime soon.