Because apparently arenanet/ncsoft hadn't finished the technology. Once they did it was just a simple act of "borrowing" that technology, and poof blizz makes an announcement. I seriously don't think that's what happened. Though I do get meh about blizz "borrowing" so much from other games. Doesn't seem fair how it is in the game market.
1. If a game company announces their "next cool thing" wow copies it, and integrates it.
2. If they don't, the fans are like "wth X Company, why aren't you giving us any info"
WoW is the Borg of MMOs. Resistance is futile, you will be assimilated.