Sightreading plays

As best as I can, that is, so long as the published text is available to me, I read it before going to the performance in preparation for it.  Now, the curious thing is, if the play as performed is two hours long, it should take me as long to read it if not well within that time.  But it always takes me longer.  I am fully aware that I am not a fastest reader but I seem to read faster when I read stories, essays, and even scholarly articles.  It makes sense that, reading a play, especially in the early portion of it, like Act I, I have to sort out as I read who is who and who is saying what in what manner of behavior.  Performed on stage, these matters are visually presented and therefore effortlessly grasped.  In fact, on certain occasions, as when I am no possession of the printed play in advance, I read it after attending the play.  Then, I read quite faster.  It still irks me that I cannot read a play in one sitting the way I can watch a play in one sitting.