Social justice and "fairness" is rarely one of the main goals of a meritocracy. The main goal of a meritocracy is peak performance. NFL teams select the "best" quarter-backs not because it's most fair, but because it will produce the most wins. Universities grant tenure to the most productive professors, because that will enhance the University's reputation. Hospitals hire the best doctors, because they can save the most lives. A society should delegate its most important responsibilities to its smartest/most-knowledgable members, because they can best lead society through worldly challenges.
Which is not to say that Social Justice isn't important. It is vital. But you don't get to it by hiring the wrong people in the wrong roles. A meritocracy excels at producing wealth - Universal Basic Income, Universal Healthcare, Unemployment Insurance, better Public Schooling... these are the kind of Social Justice programs that best distribute the wealth back to society.
When the benefits of a society that's lead well bubble up to a small elite, why should anyone else give a shit about how well-optimized the operations of society are?
To put it more directly - why should someone on the floor staff of Wal-Mart care about how optimally Wal-Mart is ran? They get paid by the hour, they don't own any stock in the company - and if it collapses, they'd just find another crappy job in another crappy retailer that pays minimum wage.
It's also worth noting that a lot of the optimizations of society are directed at 'optimizing' the share of the pie that the small elite receives.
In a well-functioning society, they should care because taxation of the small elite disproportionately funds the social safety net that means that, even though they mop a Wal-Mart, they'll get chemotherapy if they have cancer, and won't immediately become homeless when Wal-Mart deploys a floor-mopping robot and lays them off.
We don't have that, or, we don't have all of that. But we could. And historically, simply confiscating the wealth of the elite, or just stacking their headless bodies in mass graves, doesn't do great things for the prosperity of the average citizen.
Which is not to say that Social Justice isn't important. It is vital. But you don't get to it by hiring the wrong people in the wrong roles. A meritocracy excels at producing wealth - Universal Basic Income, Universal Healthcare, Unemployment Insurance, better Public Schooling... these are the kind of Social Justice programs that best distribute the wealth back to society.