Search Engine Problem

Google tends to spider my pages daily or every other day which is great. I get alot of traffic from the various headlines, however, heres the problem. Once the headline roll off the frontpage, they aren’t indexed and they stop appearing in the search results.
For instance, on Aug 1st I had a story about the terror alert in New Mexico. If you search for “new mexico terror alert” the site comes up number 2 or 3. However, it’s no longer on the main page so when Google spiders again, it doesn’t show up anywhere.
How can I get the catagory pages or story pages to be indexed?
Any thoughts
https://www.nationalterroralert.com