As much as not having them appears to suck on paper, instances are one of the main offenders of pushing the consumption rate of content up way faster than can be controlled by developers. The fact that someone can't get a group together to get achanceof getting [insert contested desirable item here] pushes that off the night's agenda, and ensures only one of that particular thing is going to enter the economy at a time. The alternative is 100's of groups doing the exact same instance killing the exact same boss at the exact same time, along with having whatever item(s) enter the world an order of magnitude faster. It lowers the perceived value of the item, your character, and the game.