For the same reason you don't hand over the keys of a Ferrari to a 16 year old kid who just passed his driver's test. Say what you want about Bale and Benzema, RM has made an 18 year old kid the focal point of the offense with the majority of action passing through his feet in the final third. And while he causes a lot of havoc, he doesn't provide the one thing RM needs most.... GOALS.
Benzema has been awful for years and Bale is a 2nd banana at best so naturally the veterans are going to get the brunt of the blame.
And people question why Madrid is struggling to win games in Ronaldo's absence.