I think it's a mixture of the effective of a great cast well timed, a thirst for really intellectual and good theatrical experiences (that aren't in 2 parts or require 7 hours of you time, or 4, like Angels and Iceman, etc), and the fact that it's a famous author and a play very few people have ever actually seen. That and good word of mouth.
In another season it might not have done so well. |