Director/Screenwriter Paul Thomas Anderson enjoys an unusually close collaboration with his actors and is able to elicit exceptional performances because:

he writes parts specifically for the actors he hopes to cast.

Explanation:

One of the most praised filmmakers in Hollywood, Paul Thomas Anderson is keen on working collaboratively with actors and producers, such as Melora Walters and Philip Seymour Hoffman, who have worked together with Anderson and appeared in several of his films.