This is interesting. It appears as though Google is losing older documents (such as 10-year-old blog posts) from its index.
I’m in two minds about this.
On the one hand, Google has long been something other than a mere web search engine, and rightly so. They want to get you relevant answers to your query. And old blog posts will rarely be the answers to many people’s queries.
But on the other hand, someone ought to be indexing the web. And if Google can’t (or don’t want to), who can?
My mental model of the Web is as a permanent, long-lived store of humanity’s intellectual heritage. For this to be useful, it needs to be indexed, just like a library. Google apparently doesn’t share that view.