You run them mostly for tomes anyways, or to gear up lesser jobs possibly. Why should dungeons drop better gear than raids? That is the progression, I thought. once you hit 50, you have WP and AK, followed by PS HK and CM. After that, or while running those, you get philo which turns into DL gear. That opens up more fights, like CT and finally Coil, which gives your endgame gear.