I'm sure the price is negotiable. Off the top of my head, the reasons you'd pay any nonzero amount of money for it are:

1. You avoid all of this drama. Christian makes a post that says, "Reddit offered me a lot of money and I said yes because I want to have a lot of money. It's been a pleasure working with them and it's been a pleasure developing Apollo for you. Peace out." Reddit ran this playbook with Alien Blue and it worked out.

2. Reddit could rather enshittify Apollo gradually, and/or fold Apollo's subscription model into Reddit's own model to maintain a premium power-user experience. It is an absurdly well-polished app, even if you added advertisements to it. It is a better user experience if the app gets worse slowly than if it disappears all at once and forces everyone to migrate to a new app. Reddit ran this playbook with Alien Blue and it worked out.