Why my number of ‘discover-not currently indexed’ links increase?

There is one problem that I may need your advice: I have pushed many links up to Google Index. At first, the number of indexed links rose fast. But then, my indexed links were gradually eliminated or unindexed, which cause the total number of indexed links decrease. Not just that, the number of discovered-not currently indexed links also increase. Now 2.091.968 of my links is in the queue but not yet processed. (Please see the photos enclosed).

Therefore, from your experience and expertise, would you be kind to help me to answer these questions:

Why my number of discover-not currently indexed links increase?

Are there any ways that I could decrease the number of discovered-not currently indexed links?

I am facing this problem while trying to decrease Crawl Time in Crawl Start section for the website address

Thank you very much for spending time reading this email and help me out. I am grateful to receive your help.

Coverage in Google Search Console Coverage in Google Search Console