If they would do so then there would be also people who would be saying they are doing a bad job because they do not follow what is written in the book. I also think that the scenes you mantioned were great. It great that the series can offer scenes that are not written down in the books, but which show us much of the background. eg littlefingers love for catelyn, cersei-robert problems, tywins relationship to jaime and so on. I just think that the mix of following the book and doing such improvised scenes is important. And in my opinion they have done an excellent job till now.