1. Because a good deal of the fun is trying to figure out how much of what they do is genuine vs. for show, whether we’re talking about Margaery’s Disney princess act, or Olenna’s crazy old woman routine, whether Garlan killed Joffrey, etc. Having a Tyrell POV would provide too many answers.
2. Haven’t read the leaks, don’t think the show and book are going to track as closely as other people do.