They can't do everything with such a small team (don't forget that besides expansion they are working on new dungeons and raids every 3-4 months), and instead of updating old stuff they prefer to invest resources into new experemental content which can be hit or miss, The Diadem and Verminion are failures, but Aquapolis was popular for a while and Deep Dungeon and Wonder Tails are big hits.
I'm more not happy with them not giving a new Frontline map in 3.5, so we'll have only 1 active (and the worst because it's PvE oreiented) for about a year. If they don't have resources for new areas, they could just reused the same map and added new PvP objectives, maybe buff/LB boxes timed spawn insead of ice crystals.