Indexing is a search engine process where search engines store all crawled data in the main server with categories so that they can provide quite relevant information to their users while they are searching on search engine result pages.
Let's Know The Top 10 Reasons Why Google Isn’t Indexing Your Website
1. Site Is Not Mobile-Friendly
2. Site Loads Slowly
3. Using Plugins That Block Googlebot from Crawling Your Site
4. You’ve Been Penalized By Google
5. Not Using A Sitemap
6. Check your website's robots.txt file to ensure it's not blocking search engine crawlers
7. Make sure that your web pages don't have the "noindex" tag