True, but make even one classification mistake (and people upload stuff they don't own with the wrong license all the time) and you have to retrain your whole system for each mistake you make, as people trickle in and want their (wrongly classified as CC or public domain) stuff removed from your dataset.
It would chill the whole ML space significantly for decades, IMO, as the only truly safe data would be synthetic or licensed. This can work for some applications (e.g. Microsoft used synthetic data for facial landmark recognition[1]), but it would kill DALL-E 2 et al.