There's reasoning and there's justification. It's entirely possible that the reason a judge does something is not revealed by the justification they present.

And judges' results are checked by appeals courts. If a judge is found to, consistently, base their decisions on some illegal bias, they can be impeached and discharged of their duties. It's unfortunate for their victims, but it's small scale.

When you move biases from one person into a whole system, be encoding them in some poorly considered model and executing it at scale, then the process of correcting it can be far more difficult (though problems should also arise much faster so it shouldn't persist as long, but that's only in theory, not practice).