The page that ranked for a query last year may answer a question people no longer ask.
Search intent drifts. A query that wanted a guide last year may want a comparison or a tool today, and the result page changes to match.
Watch the result page
When the type of pages ranking for a query changes, your content needs to change with it, even if nothing on your side moved.
Rankings fall when the question changes and the answer does not.
Takeaways
Review your top pages against the live result page every quarter, and rewrite for the intent people have now.
