That's why this whole debacle is so mystifying to me. If they would have tried to monetize the 3rd party space by way of charging a reasonable API price to the devs, it's not hard to imagine that most serious Reddit users wouldn't have any qualms with parting with a few bucks here and there to keep the status quo. I can't imagine that Reddit is able to create a situation where they earn more from their advertising platform per user than having users simply pay to maintain the existing experience.
The only theory I've heard that makes a lick of sense is that if Reddit fundamentally changes the site experience to pursue other monetization options (Hello Reddit NFTs), then 3rd party apps would've been able to just ignore implementing those features entirely.
NotTheOnlyGamer