Increasing the number of blades up to some optimum value, in this case 6, increases the maximum value of CP and the inflow velocity at which this occurs. Beyond this optimum, CP begins to decrease while the corresponding inflow velocity continues to increase. In this case, above 5 blades, the maximum values of CP occur at inflow velocities higher than desired. Increasing the number of blade will increase blockage eventually reducing the effectiveness of the turbine. Also, having more blades will result in a more expensive turbine.
