Google is not indexing all the pages, unless you have a site of 5 pages. Let’s say you have 1,000,000 pages, but google sees only 1,000. Where are the rest?
Even after submitting sitemap.xml, still the number does not increase significantly.
The reason is: the incoming links. More incoming links you have, more pages google sees. It’s a proven fact.
So, get relevant incoming ongoing links. Not hit and run