There’s no reason they couldn’t have required Reddit Premium to access the API from third-party apps. Then the app developers don’t have to deal with the burden of payment processing, Reddit theoretically earns more than it would under the API plan (the Apollo dev estimated the monthly API cost for an average user would be $2.50 (but would be much higher for actual customers due to needing to pay the Apple tax and for development costs) while Premium is $5 per month right now and already removes ads), and nobody gets angry.
Plus then you have people’s credit card information, and thus you can avoid the regulatory issues that Reddit is claiming they’re encountering with NSFW content.
The fact that Reddit seemingly refuses to even consider this option really confirms that this is being done purely out of spite over both not being able to monetize OpenAI’s training data collection plus spite over most of the third-party apps being more financially stable than Reddit currently is.