the option of money and actual money, are not the same thing. Which do you prefer, if both were taxed at the same amount?
So, the difference in tax is needed to create a motivation. Your governent sees it as a good thing to not take wage, but to invest in the company you work for. And I agree!
The option of money ultimately turns into real money and that real money is taxed at 15%. It's a means to shelter income from taxation.
History has shown that the "motivation" you speak of leads to "pump and dump" schemes and other fraud in order to leverage the free market system for personal wealth.
The wealthy don't have to pay for everything; they do have to pay for their fair share.