Why is my page “Crawled – currently not indexed” when its canonical, sitemap, links, and HTTP status are correct?

Because those checks prove Google can find and fetch the page, but they don't guarantee Google will add it to the index. “Crawled – currently not indexed” means it was crawled and Google hasn't chosen to index it at that point. First, inspect a few affected URLs and run a live test to make sure the main content actually renders for Google. If that looks right, compare the pages honestly with each other and the existing search results: thin, near-duplicate, templated, or not-very-useful pages are the usual thing to improve or consolidate. A sitemap and repeated indexing requests won't substitute for a clear reason to keep that particular page in the results; request indexing again after a real improvement, then give it time.