Under the current capitalist economic model the richer you are the more societal and material benefits you receive. This includes attaining a higher standard of public services delivered in part by the private sector. This minority do economically better out of the current economic model and can therefore afford to pay a higher rate in taxation to fund public services for the majority.
Wealthy individuals also derive the bulk of their income from fixed assets. Society and the economy are set up in a way that benefits the asset rich, while punishing those who are asset poor. The tax system reflects this bias, ensuring a lower rate of tax on dividends and shares compared to income earned through employment.