If you know impressions, clicks, and earnings, CTR & CPM are one simple division away from knowing. If someone really wants to use that information for their own evil purposes... I'm sure they know how to divide... So why?
Because its part of googles mystery...they dont like to tell us anything. EDIT: And maybe they give different amounts to other premium sites and they dont want everyone to complain or ask questions.
Well, for one, it may allow some insight into what they are paying for particular content and then that may tip of the competitors ...
This almost makes sense. I hadn't thought of that. But if they were a competitor and really going to use that info they could calculate it from the impressions, clicks, and earnings... I said that in the original post. Did you only read the title?
I honestly think it's one of the measures to protect publishers that everybody seem to believe are nonexistent. Think about how much copying of content goes on the way things are, now picture a newbie showing up here and starting one of the "OMG!! I get 45% CTR this month!!! Google gonna sure ban me!! What I should do?!? Help me please!!" threads. In 2 hours, there would be a hundred absolutely identical websites up. While you're right about being able to calculate the values yourself, I just think lazy people wouldn't bother. Between this and protecting their big publishers, I think this pretty much explains it.