The OP says Reddit claims they were being blackmailed (which clearly they weren't) but it's the talk around opportunity cost that I don't understand, especially as related alleged blackmail.
1) It would cost Apollo $20m to continue operating, and somehow Apollo, not able to afford it and offering to just kind of walk away from the app constitutes Blackmail?
2) The $20m opportunity cost claims. I don't get this. The new actual cost to Apollo would be $20m, that's not an opportunity cost for Reddit. The opportunity cost for reddit is really just the resources & attention it takes them to keep the API system running, which is presumable far, far, below the sticker price they will be charging 3rd parties per 1,000 API calls.
3) In general, I don't understand how any 3rd party has leverage to threaten or blackmail Reddit. Sure some people prefer to use 3rd party apps & services, but I'm assuming (is this a bad assumption?) that if those apps and services went away that a large majority of of their users would simply switch to native reddit options rather than stop consuming & interacting with content they enjoy.