There could be several reasons why Google finds a page that is excluded by robots.txt. Here are some possibilities:
- Configuration error: It's possible that there is an error in the robots.txt file syntax or the way it is implemented on the website. This could cause search engines to ignore or misinterpret the instructions, leading to pages being indexed despite being intended for exclusion.
- Delayed crawling: Search engines may not immediately update their index or crawl the website frequently. If the robots.txt file is updated to exclude a page, it may take some time for search engines to recognize and respect the changes.
- External links: If other websites hyperlink to the excluded page, search engines may discover these links and choose to crawl and index the page, regardless of the instructions in the robots.txt file.
- Access restrictions: Robots.txt directives are recommendations, not enforceable rules. While well-behaved search engines generally abide by these instructions, some may choose to ignore them, especially if the page is accessible to the general public through other means.
It's important for webmasters to regularly check their robots.txt file, ensure its correct implementation, and monitor search engines' behavior to detect any inconsistencies or issues.