Like it or not, Reddit wants to "improve ad performance."
I left a couple of months ago. Couldn't be happier.
The writing is on the wall. The leader thinks the Genius-with-hair-transplants is a superstar, despite destroying a globally recognised brand. Inspired by this, Spez is trying to get Reddit ready for an IPO. This means, maximise profits by any means.
The API fees clearly weren't made to make money directly though, it was meant to get rid of 3rd party clients so they could more effectively do what the OP is about.
We don't know their actual engagement numbers, what I do know is: quality on non-default subs has pitfalled. That is subjective, but its common across other reddit users I know.
Both the quality has declined, and the tone seems consistently more negative. Like there's an even bigger majority of angry teenagers running the site.