When Google crawls a page and it appears in the SE why doesn't it stay there forever? For example on my site I have galleries, I list the latest galleries on the main page, they get indexed but as soon as they are off the main page they go out of Google, but why should they need to keep getting re-indexed and crawled to stay on Google, why can't they just get crawled once and then stay in the search engines? I dont understand why they have to keep getting re-crawled?
Mostly because pages don't stay up forever so the bots have to verify that the pages still exist, reexamine who links to them and who they link to so that they know how important the page is. When you make changes to your site you expect the bots to pick up on them. You can't be selective about which changes they see and which they don't. It also means that when you search with the associated search engine you are less likely to get 404 page not found errors because the bots have been ensuring that the pages still exist.
click through rate: http://www.webmasterworld.com/forum30/33769.htm http://www.sitepronews.com/archives/2006/apr/26prt.html http://forums.seochat.com/google-op...h-affect-the-serps-in-google-80750.html?pp=10