Ok, i'll play this stupid game. Can you answer me one question - What is justice?
Justice is usually discussed in legal terms, but I guess here you're being more philosophical. So in that context, it's about an individual being rewarded/punished based on specific actions/decisions made by them.
This is a separate (but not unrelated) topic to equality and the many -isms/-phobias that are relevant to this thread.
Equality is about society. It's about power. It's about opportunity, and big-picture fairness.
Let's see if I can think of an example to highlight the difference. For the sake of argument, let's say that we do in fact live in a world filled with inequality, where being a white male gives me a better chance at getting a job, on average, compared to someone who is black, or a woman, or both (there are many other categories of inequality, but these two are well known examples).
Now, in this world there are however some companies who acknowledge this inequality, and seek to address it by pushing forward opportunities for people who are black, or a woman.
I apply for a job at one of those companies. I am skilled, and qualified. But the job goes to someone who is skilled and qualified, and is also black, or a woman, and has benefitted from these opportunities provided by this company.
This may seem like an injustice to me, looked at in isolation. And maybe it really is. However, it does not exist in isolation. As a white man, I can go to any of those other companies, the ones that do not recognise the problem in this world and do not choose to do anything to change it. At those companies, which are the majority, I can more easily get a job than someone who is black, or a woman. So in this wider world, even with this one instance of "injustice", I am still more likely to succeed. I am still at an advantage. I still have more option, more opportunities, simply because I'm a white man. So there is still inequality in my favour, regardless of justice.
Now this world I described, is of course the one I believe we really do live in. Maybe you disagree, in which case I doubt we can reach a common ground within the confines of this forum. But it's the world I see when I look around me, and the problem of inequality is the one that causes the most problems to the most people, even when you take occasional instances of personal injustice into account.
Inequality is everywhere, and it's concrete. Injustice (in this specific context) is isolated, and more often limited to thought-experiments than real-world examples.