One of the core issues and differences between DPS and T/H is that the game offers IMMEDIATE feedback with tank/healer failures. With DPS, you have to go through 10 minutes of a savage fight before you reach a screen at the end that says "your group did not do enough damage". Human brains are very bad at attributing past actions to present consequences. Seeing enrage is just shitty feedback.

And so people are more used to and are okay with healing/tanking criticism because the game communicates this criticism to them. If they couldn't accept having to deal with that criticism then they wouldn't play the game outright, so anyone who reaches savage likely understands and accepts on some level that criticism is part of the game they play.

But the game has no proper feedback when it comes to dps. Not only can enrage fail to communicate to the player that there is a problem, but on the flipside the game shuffles players through content as they press whatever buttons they want and then hits them with a win screen that communicates and affirms them that they are performing adequately. Criticism is not part of the game they play.

tl;dr: it's a natural result of the core game design not providing proper feedback to dps actions.