Several years ago, posts on my site would be indexed very quickly (usually 1-2 days after I publish them). But now, it takes 2-3 months after publish before pages get indexed.
This is not due to low quality content, because once indexed, the posts are well ranked. If I inspect the URLs of not indexed pages in Google Search Console, I find they are discovered (through the sitemap) but never crawled by Google (and of course not indexed.)
Why does this happen?