And we all know why the Heart system exists. Because, at one point, someone in design became afraid that "players may not know what to do! How do we give them something to do?".
The answer in WoW is the yellow "!" sign, and being told explicitly "go there now" (and, in various expansion, being absolutely unable to go there until told. I'm looking at you, Cataclysm). The answer in GW2 is "look at your map, and find a heart that's empty".
Yep. Because that shit is done in your Personal Story. You know, the thing that has a real quest journal, tells a story in which YOU are the hero, yadda, yadda? In which you follow a story, just like the WoW quest lines? Where you infiltrate a Dredge city disguised in a Mining Suit, try to keep alive the defenders against a massive onslaught of undead on Claw Island off Lion City, etc? You see, those kind of things exist in GW2. Just not on the map, in an instance.