I certainly feel like the protests have gone beyond the API charges.
They were certainly the instigator.
However, the continued protests came around because of Reddits attitude towards the 3rd party developers, internal Reddit memos dismissing the protests, an AMA that doubled down on these disliked opinions, further interviews that lots of redditors think showed that Reddit doesn't understand what they have/are doing (or don't like what Reddit are doing), trying to forcefully reopen subreddits to dismiss users opinion.

It's a culmination of Reddit doing strange things (video streaming, chat, NFTs) that nobody really wants, in order to try and be something they are not, then finally trying to forcefully monetize their users.

I think these further protests show that Reddit isn't as smart as it thinks it is, and has no idea what it is doing, what its market is, what its core users are...

They could have required 3rd party app access to require Reddit Premium, with enterprise access plans for AI companies.
This covers everything.
Allows the same monetisation as 1st party premium subscribers (albeit with less extra user meta data).
Age verification for NSFW API access.
Premium subscription could even be tiered to separate the modest users from the heavy users. And enterprise plans that can pay for the heavy data usage.