A WebmasterWorld thread asks, why does Google not show a page's PageRank within Webmaster Tools. The SEO asked, "The reason we all want to see pagerank is to tell how our site(s) are performing, just like all the other stats provided. Since you'd have to verify and login, its not as likley to be abused as the toolbar."
Truth be told, we know the answer. Google did show PageRank in Webmaster Tools but dropped it in October 2009. Why? Google's Susan Moskwa explained then:
We've been telling people for a long time that they shouldn't focus on PageRank so much; many site owners seem to think it's the most important metric for them to track, which is simply not true. We removed it because we felt it was silly to tell people not to think about it, but then to show them the data, implying that they should look at it. :-)
Yes, Google does not want you to "think about it" or even "look at it."
So why not remove it from the Toolbar? Well, they wanted to but I assume Google's PR team (press team) didn't want to drop it for marketing reasons.
Forum discussion at WebmasterWorld.