I've been in Bahrain and UAE for many years, income and wealth inequality is a real problem. A lot of the high earners are either sheikhs, landed nobility and business people who have large businesses in oil, energy, etc. who had opportunities open to them and could grab it while Bahrain or UAE was still undeveloped. It is also why their high earners is so high up in rankings. This coupled with the fact that these places are tax havens or pay much less tax because the govt can rely on oil revenue means you can keep a lot more of your income.

However, it seems there has been an economic downturn recently and taxes have been increasing so the economic landscape of Middle Eastern countries could change.