Michael Medved explained it well - sometimes people don't obtain extravagant wealth through sustained, difficult work - and they make the incorrect assumption that this is the rule for ALL wealth. They choose to believe that financial success in life is not because of a willingness to work hard over long years, but luck or other factors. So they feel guilty. 

That is especially true for people who have "creative" occupations. One marginally-decent actor succeeds because of luck or some other random factor, while thousands of equally talented, attractive actors end up on skid row. The successful ones feel guilty and devote their lives to curing the "injustice" they believe is not just confined to a minuscule minority of high-income earners. These dull ignorami (sic) buy into the Marxist Bravo Sierra that, "those who succeed in a capitalist system only do so because of nepotism, corruption and greed". 

Of course, NONE of these bleeding hearts give up their easy lives by divesting themselves of their wealth, they merely self-stimulate constantly with infantile virtue-signaling and endless, symbolic rituals of wholly-imagined "moral purity".