Players are being kicked already for underperforming, adding a parser won't change that. It will change that players being kicked will know why if they think they are playing adequately and ignore any advice because they think their way is good enough, then they get a loading screen from being removed from the party. Without parser they will think everyone else was in the wrong. With a parser the rest of the party will be able to say "look, you are the reason we cannot kill this, the numbers prove it. So, try that advice I gave you about your rotation and you will see an improvement."
Do you not think that players may be getting frustrated because they know certain players are underperforming, and they have no way to actually, officially prove that the underperforming player is preventing completion of the duty? They can't help people who are admant they are in the right, and without official parsers they cannot prove it that they need help.