An updated page ranks worse when the update moved it off whatever it was actually winning for. The usual culprits, observed again and again, are four: the rewrite shifted the page’s intent fit, it stripped out content that was quietly load-bearing, it re-triggered an evaluation that happened to settle lower, or it simply coincided with a broader algorithm update that gets blamed on the edit. Run the suspects one at a time.
Start with intent fit. A page often ranks because it matched the specific thing searchers wanted, even if that match was partly accidental. An update written around a slightly different angle, a broader topic, or a new keyword focus can pull the page away from the query it was satisfying, so it now answers a question fewer people are asking. The content reads better and ranks worse, because better-for-you is not the same as better-fit-for-the-query.
Next, load-bearing content. Sections that felt redundant or dated to you may have been doing real work: a paragraph that nailed a sub-question, a passage that gave the page its topical depth, a chunk of detail that matched long-tail searches. Cut it in the name of tidying up, and you cut the thing the rankings were resting on, often without realizing it was holding weight.
Then the re-evaluation itself. A substantial change puts the page back into open assessment, and the post-update settling can land below where it started, sometimes temporarily and sometimes not. This one is hard to distinguish from the others without watching how rankings move over the following weeks.
Finally, coincidence. Algorithm updates roll out on their own schedule, and a drop that lines up with your edit may have nothing to do with it. Checking the timing against known update windows separates cause from coincidence.
To diagnose your own case, put the old version next to the new one and compare what you changed against what the page was ranking for. If you shifted the angle, removed a section that matched the query, or edited right as a broad update landed, you have your suspect, and usually your fix.