This is a tired argument that needs actual evidence to go beyond the level of a conspiracy theory.
They are all very open about it. It's likely the reason why the frontier labs are ok paying many more dollars a person in compute than they receive as revenue on subscription users for now.
Here is OpenAIs page
https://openai.com/policies/how-your-data-is-used-to-improve...
>When you share your content with us, it helps our models become more accurate and better at solving your specific problems
And as a bonus here is anthropics saying the same thing
https://privacy.claude.com/en/articles/10023580-is-my-data-u...
Especially if you're doing something in a very sparsely populated part of their latent space it just makes sense that it would get used. Their biggest problem getting solved at the moment is going beyond what common crawl enables.
I await the standard goal post moving.
Its quite obviously about good/bad faith use of user data.