Google may discover and crawl your pages, but it does not mean that it will necessarily index them.
There are many reasons why Google might not index a page. Perhaps it found duplicate content. Perhaps it does not feel that it offers enough value for any specific search queries. Google may have found something about your page that it doesn't like.
Whatever the reason might be, Google just hasn't decided to index some of the pages that it has discovered and crawled on your site. It's pretty normal for some of your pages not to be indexed. Some of the pages on my sites aren't indexed despite it having better content than many indexed pages and having a substantial amount of internal links. Google's indexing system is a machine learning algorithm. And so it may decide not to index some pages sometimes for a variety of unknown reasons.