At the risk of sounding glib, they're paid the most because they're the best at convincing people who control money to pay them. Also, in no small part, becaus

At the risk of sounding glib, they're paid the most because they're the best at convincing people who control money to pay them. Also, in no small part, because in most cases the people who control the money have little or no incentive to care what happens to it, and therefore are subject to every kind of conflict of interest and cognitive bias known to man.