There are many things that would made google to Deindex your page like -
1 - Crawl Blocking Through Robots.txt File - You end up removing your URL from Google’s search result pages (SERPs) yourself if you have a crawl block in your robots.txt file.
2 - Spammy Pages - If you create suspicious pages to trick users and search engines or leave your comment section unprotected against user-generated spam, you risk removing your URL from Google search results.
3 - Keyword Stuffing - While keyword stuffing might appear an easy way to increase your rankings, you also risk having Google remove your website from search results.
4 - Duplicate Content - Google does not condone duplicate content and Google removes content. To avoid this create unique and relevant content in line with search engine rules.
5 - Auto-Generated Content -
Google removes content that is auto-generated because it:
1 - Focuses on replacing keywords with synonyms.
2 - Adds little to no value to readers.
3 - Contains errors and lacks context.