Making the world's finest brushes doesn't come cheaply. The Winsor & Newton brush factory in Lowestoft, England is home to brushmakers who 'dress' the hairs, themselves (rather than accepting brokered, pre-dressed materials). These dedicated workers are required to have at least a decade of supervised training and experience before rising to the role of brushmaker for the finest of the hand-made brushes.
These master brush makers practice skills that have been developed over the course of generations, and those skills and qualities aren't cheap. But then that's never been Winsor & Newton's goal—it's their job to make the world's finest.