That makes sense. Thanks for clarifying.
I would maybe add that they might come back into squeezing out all the ad money only if they manage to maintain the monopoly over the distribution/attrition. Which I'm not sure is that certain.
Any of the clients who manages to eat up some of their user share is shrinking their pie. Moreover, can vastly undercut their "distribution fees".
They have to keep up the relevance and quality high in order to afford balancing something out of it in their feeds with ads. For new clients, getting the quality is difficult, but they can undercut their ad fees (ad share) without a tear.