I only read from the Apollo guy, that the amount of requests the users of his app make, would get him to pay reddit 20 million a year. So, the more popular your 3rd party app is, the more they would have to pay Reddit.
The one i use, Sync for Reddit, is also dying before the 1st of July arrives. From there on, the new prices apply.
Reddits motivation for this, is to get paid for API access by companies like ChatGPT. They suck reddits content, our posts, in order to feed the AI with content. I assume they do it big style and Reddit wants to cash in for this.