I am/was in a situation like that.
I had many pages on Instagram (was on many admin as well), monetization was never a problem, but currently it's just harder. Back then, we've been contacted multiple times a day for shoutouts, today I'm happy to get 2-3 DMs a week ^^
To be fair, I'm probably investing 3 hours / month into Instagram, hence it's clear why I'm making less money. I even opened a thread on here to ask for help how to get new customers.
To keep things short, I just think that some people basically don't want to continue Instagram or don't know what to do with the page.
//BTW: The 100k account I mentioned, which was purchased by two "friends" of mine, has reached 700k a few days ago. (~+600k in less than 6 months

)