The claim of the book is that you, as a regular investor, do not have access to better-than-market returns, not that they are not possible. Anyone who can provide better returns will claim the difference for themselves (in fees) rather than pass it on to you. Why would they give you free money?
Let's say that funds X, Y, and Z can regularly beat the market. Fund X then passes on better returns to its customers, and therefore gets more customers. Then Y and Z have to do the same thing, otherwise they lose customers. Simple competition.
