Because a graduated tax rate is more fair.
To tax people who are barely making it the same as people who are making 400 times that is a receipe for disastor.
It is another load of bull you have been handed and lapped up like so much pablum.
the reason it will never happen is that rational people know simplicity doesnt mean success
So equal LAW for all citizens just goes OUT the window in your world...and along with it LIBERTY, and Free Will...?