Sorry, if this is a naive question, but I could not find the justification in any of the major text books like Bondy-Murty, Diestel or West. Perfect graphs have many beautiful properties, but what is the single reason they are called perfect? Or is it just a aesthetic preference by Berge?
perfect graphs were first motivated by information transmission theory originating with Shannon ie Shannon Capacity of graphs. they are called "perfect" by Berge because they can be used to model a noiseless or "perfect" information channel wrt transposition errors in transmission called "confounding". from intro in  which also has a very detailed history in the 1st chapter cowritten by Berge.
 C. Berge, The history of the perfect graphs, Southeast Asian Bull. Math.
20, No.1 (1996) 5-10.