Bluesky released a statement today about data use [0] - saying they will not use your data for "Generative AI" (surely in response to X's recent change to say they will).
As you imply, this is a bit meaningless for people who don't want their posts used for AI, because anyone can grab all data pretty easily (at least for now).
But, AI aside, this is so much better for a lively ecosystem - 3rd party apps, bots (the fun and useful kind), research, etc. A lots of things simply died when Musk decided effectively end the API program [1].
[0] https://bsky.app/profile/bsky.app/post/3layuzbti6s2x
[1] https://www.wired.com/story/twitter-data-api-prices-out-near... == https://archive.ph/ikPOk