One of my website has 500,000+ webpages, and I started to see that the SERP ranking of such pages started to be eroded with the time. I've been checking, and around 10,000 of the webpages had no visit in the last six months. I've read about the concept of "Crawl Budget Optimisation", and I'd like to know your opinion: Can the ranking-drop be related to the Crawl Budget? Is it worth inserting a "<meta name=robots content=noindex>" tag in each one of the pages with no visits? Any recommended tool to handle/automate the server logs? Thank you very much.