Also such debuff would benefit melee in many areas. Especially if it could be applied to yourself (e.g., buff: all ranged offensive attacks have reduced range against you). PvEwise, now many mobs tend to ignore what seems to be wall (los) and nuke straight through it, or stand in middle of heavy AoE refusing to move (like those Mogu rares). it could be useful and nice in such situations as well.
Because playing melee in current WoW is extremely frustrating. Having such abilities would make their lives more bearable in many circumstances, meanwhile casters still wouldn't have to deal with horrors of playing melee.Casters are not supposed to be up close by any means, and that's a given because they avoid melee classes like the plague.