The separation of powers between the shareholders and managers$/$directors is imperative and justified under many grounds. One of them is that

i$.$ the dispersed shareholders cannot effectively engage in governing the corporation.

ii$.$ the dispersed shareholders can effectively engage in governing the corporation.

iii. the shareholders may prefer to long$-$term interest overlooking the short$-$term sustainability of the corporation whereas directors approach is to maintain a long$-$term interest of the corporation.

iv$.$ the long$-$term interest of the corporation is not essential for social welfare of the economy.