Why not equal tax? Because it wouldn't be equal. 20% of a low wage earners income is a substantial amount that directly impacts their ability to buy food, pay rent, etc. 20% of a high wage earners income will NOT impact their ability to buy food or pay for their home. Big difference, one is struggling to survive, the other deciding if the house staff should have to pay for their own dry cleaning.
It's like saying the
oil companies 'only' made a 10% profit last year. But the numbers are SO huge that 10% is the elephant in the room that 'rich' people tend to ignore.