It's simply faster to die since the group'll have to run back after the shade thing is dead anyway. One person will rally while the others sit there with their fingers up their ass waiting.
So you're making people wait for no god damn reason at all (a 2s repair oh noeeeees!). You're being selfish and for that alone I'd kick you regardless of how good you are.
Let's go with this example:
Everyone's dead and one guy is defeated and tries to kill the shade. After a minute he kills the shade and moves on. Now the group rezes and runs back which takes another 30s.
Everyone's dead and one guy is defeated, he let's him self die and does so 5s later. Everyone rezes and runs back which takes 30s.
Those are best off scenarios where the shade is nearly dead and thus killed fast. I've seen people fight it for over 2min, I've seen people not kill it at all (which really pisses me off) and ofcourse I've seen the combination of taking 2min and then failing.