Because the people at bungie are lazy as hell. The main difference between shockwaves and grenades to self revive however, is that self revive is the main selling point/ main reason to use a warlock. Are you only going to use a hunter because your blade dancer can release Shockwaves? Maybe there will be one or two people out there, but for the majority no. If a titan can self revive and have all these different perks and classes as well, (bubble specifically) then why would anyone bother pick a warlock over a titan? I like all the other ideas however, just not the self res.