If I had an app with 1.5 million monthly active users and the platform I piggy- backed off asked me to pay them $20 million yearly for the privilege, I would start asking VCs for money to pay the bill and hire a couple folks to build the platform my users are going to migrate to before someone else does.
Reddit the company has shown to completely misunderstand the userbase that created their website and they're slaughtering it to make a buck to payoff their own investors. So why not prove them wrong and do it yourself?
I agree. The Apollo dev arguably owns the user last-mile. It wouldn't be a stretch to offer users an alternative. Reddit was open source until 2017 (https://github.com/reddit-archive/reddit) so most of the heavy dev lifting is already done. The major cost would be in infrastructure.