It's because of Google. Google take time to Index url.
If its showing Crawled - Currently not Indexed,
means google decide not to index that page because of content quality. You can improve content quality, unique content. and then you can index manually.
and If its showing - Discovered - currently not indexed
means Google knows about that URL but hasn't yet crawled or indexed it. Google will Index that url but when its not mentioned, they can index in a week or in a month..
Google policy very difficult...
I have 2650 article but now index only 1370...
so you have to wait for indexing in google.