Because those who always rank high in percentage receive high-quality resources. This has nothing to do with the total amount of social material resources.
But truly, the world will not be fair because people are different in every strata both in size, mental acuity and knowledge etc. So this will give rise to different choice to life and different ways to achieve it. Achieving it is also a function of the kind of different environment available for different people. In other words, even the environment is not uniform and therefore not fair too. Thoughtfully, there is no way that the world will be fair with the nature of the environment and policies people made as rules to be able to conquer their environment. That is why you will have different kinds of governance system, culture, rules and laws, every other thing has to be different from the experiences of different people and the way they interpret or react to situations.
This is true: some rich kid born in an elite UK family, versus some kid in a poverty-ridden area, will not have the same opportunities even if life were fair to them both. In fact, even in the same jobs, two people will not be the same; life throws different things at them. At the end of the day, life is not fair, and that will cause differences to begin with.
We put an even larger gap ourselves meanwhile, because politics, bribery, and bad people all end up making the gap even bigger by doing things that they should not do.