The Malorne set is Druid Tier 4. All tier sets (and some other things) have a set bonus when you have a few pieces of the set equipped. For Feral Druid T4, the 2 piece set bonus (2t4) is a 10% (?) chance to gain 10 Rage or 20 Energy on every hit. This is a bigger boost to the amount of damage you can do than pretty much any single piece of gear.
As you level past 70, the % chance to get Energy / Rage back (a proc), will decrease, making the set bonus much less valuable so level 80s aren't picking level 70 gear over the new level 80 gear.