The most fundamental one is this: capital is mobile, people are not.
If you increase taxes on capital, it will flow to a lower-tax jurisdiction relatively quickly. A decent legal system and financial infrastructure is necessary, but the hurdles aren't as great.
But if you increase taxes on salaries, people will be hesistant to leave for personal reasons (e.g. friends, family), cultural reasons, security reasons etc.
As such, tax competition between jurisdictions on capital is much more fierce than it is on labour. This is typically why you see lower taxes on capital.
The other reason is that labour tends to be viewed by part of the voter base as a normal tax, and capital as a double tax. i.e., if you earn $100k a year and save much of it after taxes, you now have capital to invest. And getting that capital taxed again is sometimes viewed as even less popular, a sort of tax ontop of tax, particularly as these wealthy people are more mobile and can more easily choose a lower tax jurisdiction.
As for the notion that his capital doesn't create jobs, I don't know if that is true. Fact is that if people like him withdrew their capital from the market, rather than invest it, you'd see many financially-constricted companies that would bin their expansion plans, cancel their investments in R&D, withdraw from new products and markets etc, and on the whole, generate far fewer jobs. It's essentially what the credit crisis looked like. The notion investments like his aren't creating jobs seems erroneous.
That doesn't mean I'm a fan of low capital taxes, by the way. But tax reform is incredibly complex because it requires essentially all countries around the world to work together, to give up some control over an important component of sovereignty (taxation), to restrict tax competition somewhat. There's been a lot of decent work in that regard already by the way in the past few years, with the worst aggressive tax planning and tax havens being dealt with (e.g. BEPS), which allows countries to implement more sensible taxes on capital without worry of their tax base shifting abroad.