There is diminishing returns on how hard someone at a higher income level is effected, versus those at a lower level, in terms of taxation. This is likely caused by the cost of goods and services not scaling along with taxes. So, basically a family living on $50k being taxed 20% are not at $40k to live off of. Then you factor in all of every days costs of living, bills, groceries, unforeseen needs, etc. and you quickly diminish anything left. Now, think of someone at $500k instead, they are taxed the 20% so we are down to $400k. They are then paying the same amount for all of those items, so it takes far less of what is left. Sure, theoretically that gives them additional funds to spend back into the economy, but it does not always work out that way. Instead, they end up with more money at the end of every year, resulting in the ability to save/invest higher amounts of money, which causes exponential growth of wealth and deepens the divide further.