Why? because Google is trying this whole knowledge base search engine and it is not ready for prime time. So they try, it doesn't work so they revert to an older set of data and then they try again a few weeks later. In the meantime, the traditional search results are ignored and so things gradually decline. Notice how the shallow sites seem to do well. The knowledge engine can handle a page or two. Give it a thousand pages and it goes DUH? Go look at your site results and you will see interesting things. I know we have thousands of different products and I was amazed when I saw Google was putting the title as Details | Widget(general term). Details was just the anchor text - like click "Details" for more specifics. Google is trying to outsmart the BH spammers and losing while killing everyone else in their quest.