In "Animal Farm", why did the pigs get the job of teaching and organizing?

According to the text of the novel, the pigs are smarter than the other animals. However, the pigs are not as selfless as Old Major, the boar who originally predicted the revolution and died before it occurred. The pigs, especially Napoleon, Snowball and Squealer, condense Old Major's dream into a political philosophy called "Animalism" and proceed to take over the job of directing and organizing the other animals. However, as they continue to remain the supervisors, they do no physical labor, and they take extra food (milk and apples) for themselves instead of sharing with the others.