It's always up to the masses to demand fair treatment, or to directly seize assets. The people with power and their own armies will take what they can, others have to stop them.
Wealth inequality is increasing because we're allowing the ideas of trickle-down and magical job creators to take hold, as if prosperity is impossible without giving the rich extremely favorable treatment. And as if they're irreplaceable. If they leave over having to pay enough tax for society to be able to pay for its services and programs, somehow no one else will know how jobs work, including the many, many people who worked in those jobs and varying levels of management.
And as if others wouldn't take advantage of the market that's opened up by those who leave.