Proportional fines are not a means of revenue, where did you get that stupid idea from? Fines are punishments.
Because "Revenue Raising" is a popular conspiracy theory used by speeders in order to avoid admitting what they do is wrong.
Fines are punishments. As such, if the punishment doesn't reach even 1% of the money you earn in a day, you can effectively ignore them always, and in the process possibly endanger others. The proportionality of the system is to level the playing field, but that is clearly communism and can't be had in the united states of money.
Fines are punishments, but as you said they're only punishments up to a point. This is why most western nations have a demerit point system. If you accrue too many points you lose your license. A craw that sticks in the sides of the revenue conspiracy theorists in Australia is the fact we long weekends are "double demerit weekends", not "double fine weekends". So if you get caught doing 30 over in my state, its a $800 fine and 6 points. Do that on a double demerit weekend and its an $800 fine and a suspension (12 points). In Germany higher speeding fines come with automatic suspensions.
I dont speed, not simply because its stupid and costs money but because I also race my car, track, drift and on occasion, rally cross. After this you begin to realise that doing 15 over isn't just silly, it's boring compared to sliding a car round a track.