This is an interesting point. I use free Apollo, and realized when I tried to post, that its a paid feature.
So you have to figure that all the revenue is largely from contributing users and the dynamics on social media go something like 5-10% of people post all the content. Also, i heard it has great tooling for mods as well.
We'll see how big of a blow this is but yeah, you're right, a lot of Apollo users are probably high value reddit users.