A lot of the older raids don't seem to be run very often. I think it has to do a lot with how their items were not updated when augment slots were added to some named loot (but not most raid loot, for some reason).

Another way to increase the number of raids run would be to add new items to their loot lists. For example, CitW has nothing except for weapons. Adding new weapon types, armor or other types of equipment would entice people who already have their weapons from CitW to run the raid again. Increasing the number of commendation of heroism drops would help, too.