What is Rawls' Difference Principle? Why do people say it is not egalitarian?

John Rawls' vision of distributive justice entails his Difference Principle. The Difference Principle permits diverging from strict equality so long as the inequalities in question would make the least advantaged in society materially better off than they would be under strict equality. 

For example, his inequality aregument for tax incentives shows this. He says that if we reduce the taxes of rich productive people, they will be incentivised to work harder for more hours. This will in-turn increase the tax yields even if each each individual’s income is taxed at a lower rate. For example, assume two individuals, Allen and Benny. Allen is a productive worker and Benny cannot work. Allen gets paid ten dollars an hour. If he is taxed at fifty percent he will work for eight hours, resulting in forty dollars for Allen and forty dollars for Benny. If the tax rate is reduced to forty percent, Allen has incentive to work longer hours and chooses to work for twelve hours. Now, Allen’s benefit is seventy-two dollars and Benny’s benefit is forty-eight dollars. In the latter situation, the inequality is greater but Benny, the least advantaged individual has benefited. So Rawls argues that in some cases, inequality is permissible - only when it advantages the worse-off! 

This is an example of how Rawls (a famous egalitarian) has been questioned for his difference principle that allows for inequalities.