Um, because they both do the exact same thing and fulfill the exact same purpose. RP dump that procs rune regeneration talent. One is ranged and one isn't. One has flavor, one doesn't. The only thing that is bad about DC at the moment is that it doesn't proc some of the melee things that rune strike does, it's 40 RP cost and it's damage at low vengeance. Considering it's being put to 30 RP in the expansion I can't see how it's not a fair trade at all.
If you have to remove abilities it's a pretty good idea to remove things that basically fulfill the same ability, and it's also best to get rid of the least iconic one. Having two RP dumps isn't really necessary, but limiting us to the melee version over the versatility of the range one isn't fair at all. People mentioned they would rather have DC and we got it.
I don't see how it's not fair at all, lol.