Discord, Instagram, Snapchat, Clubhouse and TikTok have decided to ban third-party apps. Twitter and Reddit decided to charge for it.
In this case with the developer of the third party Reddit client, unless he is making enough to cover the API costs, then it make no sense to build on someone else's API with little to no revenue. That is the risk.
It is no different to TapBots (creators of TweetBot) doing the same mistake.