Sometimes one of your unlucky teammates is just going to get incapped by the tank.And it only takes two punches, ie 5 seconds, for the tank to kill someone on the ground. Not much time to go in and spam it in the back. Even if you do, there are cases when trying to save the downed survivor, teammates rush in and try to draw the aggro away, the tank decides to switch target suddenly and backhand the irritating fly standing a few steps behind it.
I have seen cases where one guy on the ground quickly leads to more because they wanted to prevent a death. It's simply better to make good of your chances most of the time.
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