That's not true. Copyright applies whether the author says so or not. By default, anything you find on the publicly accessible web, you are NOT free to reuse.
That's why the GenAI companies try to talk their way out by claiming training is "Fair Use". It means they acknowledge that the materials they use are copyrighted and not legal to reproduce without a license.
That's why the GenAI companies try to talk their way out by claiming training is "Fair Use". It means they acknowledge that the materials they use are copyrighted and not legal to reproduce without a license.