A lot of people in different subreddits and Twitter are talking about this indexing issue. So if you are also going through the same, we all are in the same boat.
Some of the theories around why it's happening - (Considering it's not a new blog/website in a sandbox)
GPT3/AI Content - One of the significant theories everyone has about this is that too many websites are pushing AI-based content, which isn't edited by a human and makes the content either irrelevant or just another repurposed article on the internet.
Content quality - It's not only AI content, but most AI tools just take the headings and subheadings from page 1 and expect you to create a similar content covering all those.
Google itself is broken - A lot of people believe that google itself is broken, and they are trying to fix things from their end.
Some of the ways around it -
Internal Linking - Internal linking it from the page, which gets a lot of organic traffic and has a good amount of backlinks.
Homepage - Internal link new articles from the homepage as google bot visits home page a lot.
Social Media - Things like GMB posts, Pinterest posts, youtube links, and Twitter posts that get indexed by Google can give it a push.
Paid ads - Earlier, doing google ads used to push the indexing faster, but not so much now.
Podcast Links- This is the only method I can swear by. I have tried the same on so many different websites/blogs, and it always worked. The podcast gets distributed to 50+ websites which creates 50+ No-follow backlinks overnight. The URL gets indexed within 48 hours of doing the same.
Let me know if you have any other theories on why it isn't working or tips on making indexing faster.
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Indexing Issues?
One tip I would like to add - Sometimes indexing issues may occur when your content is so too close to each other especially the text. Try changing the text spacing or a theme (in case of frequent indexing issues). Also, sometimes the H2, H3 tags are the culprit and may not have enough spacing in the eyes of Google bots (they don't have eyes though) so in that case try adding spacing block if your site is on WordPress