The trick is that life is a series of "opportunities" and equality of opportunity at any particular point of choice generally results in perpetuating any imbalance of opportunity that has occurred before that.
For the sake of illustration, assume two large groups of kids who innately would have had identical ability, but one's growth and education is (on average) more stunted because their families are more likely to be single parent families, or have a parent in jail, or just very poor (which affects a lot), so right now they don't have identical average ability because they did not get equal education and support some decades ago.
If you want to have equal representation of the groups, you'd have to artificially correct for all the previous differences in opportunity - without a time machine, you can't actually fix the differences in their skills and experience (no matter how fairly or unfairly those differences came to be), you can only pretend that those differences don't exist. And so we come to the core issue that granting equal treatment to unequally capable candidates means granting unequal treatment to equally capable candidates, there's no way around it.
And there's also a gap between treating individuals fairly and treating groups fairly. You can't/don't measure the opportunity differences on an individual level, but on a group level, and individual variation in opportunity is huge. In general, any "compensating opportunities" happen at a group level, because if one group is underrepresented under a "background-blind" schema, then it's because lots and lots of capable individuals from that group have "filtered away" and gone on to very different life paths long before applying - and any corrective action or quota system is not helping those individuals who suffered most from the lack of earlier opportunities (because they're already "out"), instead it's granting a larger (compensating) opportunity to other individuals who just happen to be from the same group but had enough opportunity to "stay in the game", while individuals who personally have had so-so opportunities get punished if they happen to come from a group that (on average!) has more opportunities.