Traiting existing spells would have been less effort and achieved the same goal, and since developers are human, the laziest option is usually what you'd go with (I kid).
The new DPS skills were partially added to add new, flashy animations, but mainly to fill in niches that were missing in the classes' kits while performing their roles in duties. WHM's kit for example had almost all of the HP restoration tools you could ever ask for. They were mostly just missing a reliable emergency heal, which they got with Tetra. Asylum feels like they just wanted WHM to have a bubble too. I don't really think we needed any more AoE regen, and would have preferred it to mitigate damage, but hey I'm not going to turn my nose up at free healing. Assize was a spicy new piece of amazing hotness that fulfilled the same niche as SCH's new Indomitability skill (that is, instant burst AoE heal) that could be flip-flopped to be an AoE Nuke, depending on your stance at the time of cast.
What WHM was REALLY missing (beyond mitigation skills, but that's a different discussion...) was a native AoE DPS option that wasn't Holy (expensive, not always mana efficient to cast), and a way to apply a DoT without having to manually cast Aero 2/Aero on everything. Enter Aero 3. Aero 3 being an AoE is pretty meaningless in most of the solo content you have to do in the game. Heck, Aero 3's duration is longer than most enemies will live than if you just used one of your Stone spells.
The damage component on Assize falls into a similar trap, too - you are rarely ever fighting large groups of enemies when soloing as a healer. Assize gets a pass though because 1) it's free damage (or healing) either way; and 2) it's an absolutely awesome skill that they'd have to pry out of my cold, dead potato hands.
Then we have Broil/Stone 3, which are just direct upgrades to their respective single target nuke. Really the only DPS skill that would have been required outside of duties.