The raid is supposed to be a puzzle you have to explore and discover. If they were to implement bounties into it, it would result in some of the puzzle being uncovered. Take the templar for instance: If you kill him without him teleporting you unlock a chest. If the bounty told you to do that people would have been even more like to find it, also people who hadn't played before would know the templar can teleport. Or crota, I had no idea what an oversoul was at first. Its a great idea, but sadly idk if bungie cares about good ideas anymore