Because it reduces people to a set of identity classes that fill respective identity checkboxes. I.e. if it happens that on conference there is 10 good presentation submitted from class X but only 2 from class Y, and the quota is half-half, you would either reject 8 good presentations or add 8 crappy ones, just to fill identity checkboxes and achieve equality of outcome. Or cancel the conference altogether.

The true equality would be when the conference organizers see 12 good presentations, and don't even think to dig into what identity class they represent (unless the conference is specifically organized to represent identity classes). When did you last seen statistics about hair color or eye color of conference presenters? How about blood type? Maybe AB- people are underrepresented? You get the idea.