If you interview 10 people for one job opening, you have to pick one of them. If 5 of them pass the technical interview you start filtering them on other non-technical things. "Would I like to hang out with this person", "were they funny", "do they have similar hobbies to me?", "did they go to the same school as me?"

Whoever you pick, for whatever reason, didn't take an opportunity from the other 4 qualified people.

Heck, my wife would have a pile of resumes to go through and she only read them until she found 5 people she wanted to call. If you were "the next" person in the pile it was just bad luck that you didn't get called. The people in the pile before you didn't take your opportunity.

Interviewing is hard. People don't have a "technical skill" stat that you can sort by and just take the best one. People interviewing people is a terrible way to decided if someone will be a good fit, but it's the only way we have.

Often you end up with a bunch of people that you feel are equally qualified and you just have to pick one. If you use "dei" to pick rather than "this person was in the same fraternity as me" that's just a different side of the same coin. The difference is that before DEI programs, the people that passed the "post technical" part of the interview were the people that were most similar to the interviewers (that's human nature) and the interviewers were mostly white guys.

Rather than taking away opportunities, DEI takes away the ability for white people to "always win ties"