Imagine a scenario in which DPS players would stubbornly complain that it’s not their job to avoid damage.
They would argue that their only job is to do damage and avoid instant death mechanics, but if a fight’s mechanic isn’t a one-shot, then it’s the healer’s job to top their health bar. All they want is to do damage.
Of course, the example isn’t an exact comparison of this complaint, but it’s quite similar.
Can a DPS play ignoring non life threatening damage and letting the rest of the group take care of it for them? of course. Actually, many people plays like that in casual content.
Yet, as the difficulty progresses, it’s only natural that the group will prefer someone who avoids unnecessary damage, while doing their damage at the same time. It benefits the group and it’s a sign of a better player. In the end, it helps the group focus their performance on finishing the run quicker.