They're just desperate for reward drops that they'll continue to never use because they're busy trying to clear content as quickly as possible. You can't really stop them, but you don't have to revive them when they inevitably die. These players often believe they're better than they actually are and will get themselves killed. If you're lucky and this happens in a "darkness zone", just dance on their Ghost until you're killed too and start the encounter over again. That's being really spiteful of course, but as they love to say: you can't tell me how to play.