So you don't understand income tax at all.
Most countries do the same:
a) Buy the vote of the masses, hence [near] 0 tax up to half a million a year, that where many Farang retirees are BTW,
b) Be subservient to the power of money, by implement all sorts of tax evasion schemes for the rich,
c) Hit the middle classes as hard as you can, as they are not too many voters and neither do they have the power of big money.
Doubt there are many rich amongst the LTR holders, the are mostly the middle class. I's be paying close to one quarter of my income if I had to pay here.
I have always hated the progressive income tax systems, because it hurt me when I was submitted to it, but also just for what it is: an incentive for mediocrity and laziness. Ronald Reagan is one of the few rulers who could see this and do something about it. Even though he never managed to get a true flat IT implemented.