It's easy to say "It's a roulette, take what you get", but there's occasionally groups where one person can drag the entire team down over and over again and no one wants to kick them because they don't want to be mean.

For an example, back in EW before the dungeon shortcut changes, I had a Malikah's Well run where the healer kept running into the middle of the cross pattern AoEs of the last boss and instantly dying, we had no res caster and the tank was a DRK, the healer was also entirely silent and any attempt to help didn't work. So we wipe because healer died, ran all the way back, just to see the healer dive at the cross AoE and instantly die again, what could you even do in that situation besides leave?