How are the fees prohibitive?
From the same AMA linked above:
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Free Data API
Effective July 1, 2023, the rate limits to use the Data API free of charge are:
100 queries per minute per OAuth client id if you are using OAuth authentication and 10 queries per minute if you are not using OAuth authentication.
Today, over 90% of apps fall into this category and can continue to access the Data API for free.
Premium Enterprise API / Third-party apps
Effective July 1, 2023, the rate for apps that require higher usage limits is $0.24 per 1K API calls (less than $1.00 per user / month for a typical Reddit third-party app).
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So users are happy to pay, say, Netflix $15 a month, but are outraged when Reddit tries to charge heavy app users $1 a month?